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	Author	Nikolaev, A.V.; Michel, K.H.
	Title	Electronic structure and electric quadrupoles of a polymerized chain in solid AC₆₀			Type	A1 Journal article
	Year	2001	Publication	Solid state communications	Abbreviated Journal	Solid State Commun
	Volume	117	Issue		Pages	739-743
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York, N.Y.	Editor
	Language		Wos	000167538300010	Publication Date	2002-07-25
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0038-1098;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	1.554	Times cited	10	Open Access
	Notes				Approved	Most recent IF: 1.554; 2001 IF: 1.381
	Call Number	UA @ lucian @ c:irua:36881			Serial	1009
Permanent link to this record



	Author	Lynden-Bell, R.M.; Michel, K.H.
	Title	Translation-rotation coupling, phase transitions and elastic phenomena in orientationally disordered crystals			Type	A1 Journal article
	Year	1994	Publication	Reviews of modern physics	Abbreviated Journal	Rev Mod Phys
	Volume	66	Issue		Pages	721-762
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York	Editor
	Language		Wos	A1994PG73600003	Publication Date	2002-09-05
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0034-6861;1539-0756;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	29.604	Times cited	128	Open Access
	Notes				Approved	no
	Call Number	UA @ lucian @ c:irua:9359			Serial	3702
Permanent link to this record



	Author	Copley, J.R.D.; Michel, K.H.
	Title	Multiple orientational order parameters in solid C₆₀			Type	A1 Journal article
	Year	1997	Publication	Physica: B : condensed matter T2 – International Conference on Neutron Scattering, AUG 17-21, 1997, TORONTO, CANADA	Abbreviated Journal	Physica B
	Volume	241	Issue		Pages	454-455
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The transition Fm (3) over bar m -->Pa (3) over bar in solid C-60 is driven by the condensation of orientational modes belonging to X-5(+) irreducible representations (irreps) of Fm (3) over bar m. Taking into account irreps up to the manifold l = 12, we have studied the primary and secondary orientational order parameters loops). We have numerically solved the coupled molecular field equations for these oops and calculated the temperature dependence of Bragg reflection intensities. (C) 1998 Elsevier Science B.V. All rights reserved.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Amsterdam	Editor
	Language		Wos	000074062600130	Publication Date	2002-07-25
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0921-4526;	ISBN		Additional Links	UA library record; WoS full record
	Impact Factor	1.386	Times cited		Open Access
	Notes				Approved	Most recent IF: 1.386; 1997 IF: 0.991
	Call Number	UA @ lucian @ c:irua:104360			Serial	2228
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	Author	Verberck, B.; Michel, K.H.
	Title	Anisotropic packing of C-70 molecules in carbon nanotubes			Type	A1 Journal article
	Year	2007	Publication	Physica status solidi B-basic solid state physics	Abbreviated Journal	Phys Status Solidi B
	Volume	244	Issue	11	Pages	4279-4282
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000251355800092	Publication Date	2007-10-19
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0370-1972;1521-3951;	ISBN		Additional Links	UA library record; WoS full record
	Impact Factor	1.674	Times cited		Open Access
	Notes				Approved	Most recent IF: 1.674; 2007 IF: 1.071
	Call Number	UA @ lucian @ c:irua:67350			Serial	128
Permanent link to this record



	Author	Michel, K.H.; Verberck, B.
	Title	Rigid-plane phonons in layered crystals			Type	A1 Journal article
	Year	2012	Publication	Physica status solidi: B: basic research	Abbreviated Journal	Phys Status Solidi B
	Volume	249	Issue	12	Pages	2604-2607
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The determination of the layer number ${\cal N}$ in nanoscale thin layered crystals is a challenging problem of technological relevance. In addition to innovative experimental techniques, a thorough knowledge of the underlying lattice dynamics is required. Starting from phenomenological atomic interaction potentials we have carried out an analytical study of the low-frequency optical phonon dispersions in layered crystals. At the gamma point of the two-dimensional Brillouin zone the optical phonon frequencies correspond to rigid-plane shearing and compression modes. We have investigated graphene multilayers (GML) and hexagonal boron-nitride multilayers (BNML). The frequencies show a characteristic dependence on ${\cal N}$. The results which are represented in the form of fan diagrams are very similar for both materials. Due to charge neutrality within layers Coulomb forces play no role, only van der Waals forces between nearest neighbor layers are relevant. The theoretical results agree with recent low-frequency Raman results on rigid-layer modes [Tan et al., Nature Mater. 11, 294 (2012)] in GML and double-resonant Raman scattering data on rigid-layer compression modes [Herziger et al., Phys. Rev. B 85, 235447 (2012)] in GML. (C) 2012 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Berlin	Editor
	Language		Wos	000312215300072	Publication Date	2012-11-19
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0370-1972;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	1.674	Times cited	1	Open Access
	Notes	; This work has been supported by the Flemish Science Foundation (FWO-Vl) and the Bijzonder Onderzoeksfonds, Universiteit Antwerpen (BOF-UA). ;			Approved	Most recent IF: 1.674; 2012 IF: 1.489
	Call Number	UA @ lucian @ c:irua:105992			Serial	2907
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	Author	Michel, K.H.; Verberck, B.
	Title	Theoretical phonon dispersions in monolayers and multilayers of hexagonal boron-nitride			Type	A1 Journal article
	Year	2009	Publication	Physica status solidi: B: basic research	Abbreviated Journal	Phys Status Solidi B
	Volume	246	Issue	11/12	Pages	2802-2805
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Starting from an empirical force constant model of valence interactions and calculating by Ewald's method the electrostatic force constants, we derive the dynamical matrix for a monolayer and for multilayer systems of hexagonal boron nitride (h-BN). Solution of the secular problem leads to the corresponding phonon dispersion relations. The interplay between valence forces and Coulomb forces is discussed. A comparison with previous results on graphene and graphene multilayers is made. Our spectra on the h-BN monolayer are rather similar to previous ab initio theory results. Comparison is also made with Raman and infrared experimental results.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Berlin	Editor
	Language		Wos	000272904100091	Publication Date	2009-11-12
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0370-1972;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	1.674	Times cited	10	Open Access
	Notes				Approved	Most recent IF: 1.674; 2009 IF: 1.150
	Call Number	UA @ lucian @ c:irua:80673			Serial	3609
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	Author	Michel, K.H.; Verberck, B.
	Title	Theory of phonon dispersions and piezoelectricity in multilayers of hexagonal boron-nitride			Type	A1 Journal article
	Year	2011	Publication	Physica status solidi: B: basic research	Abbreviated Journal	Phys Status Solidi B
	Volume	248	Issue	11	Pages	2720-2723
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Taking into account covalent, Coulomb and van der Waals interactions, we construct the dynamical matrix and calculate the phonon dispersion relations for multilayer crystals of hexagonal boron-nitride. Coulomb interactions account for a strong overbending of optical phonons. Applying and extending Born's long-wave theory to the case of multilayer crystals, we calculate the piezoelectric stress constant equation image as a function of the number of layers equation image. In agreement with group theory, we find that equation image for equation image even; for an uneven number equation image of layers we obtain equation image, i.e. the piezoelectric constant decreases as equation image.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Berlin	Editor
	Language		Wos	000297517100069	Publication Date	2011-10-18
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0370-1972;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	1.674	Times cited	13	Open Access
	Notes	; Discussions with G. Heger, B. Partoens and F. M. Peeters are gratefully acknowledged. This work has been supported by the Flemish Science Foundation (FWO-Vl) and the Bijzonder Onderzoeksfonds, Universiteit Antwerpen (BOF-UA). ;			Approved	Most recent IF: 1.674; 2011 IF: 1.316
	Call Number	UA @ lucian @ c:irua:94034			Serial	3618
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	Author	Michel, K.H.; Verberck, B.
	Title	Theory of the elastic constants of graphite and graphene			Type	A1 Journal article
	Year	2008	Publication	Physica status solidi: B: basic research	Abbreviated Journal	Phys Status Solidi B
	Volume	245	Issue	10	Pages	2177-2180
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Born's long wave method is used to study the elastic properties of graphite and graphene. Starting from an empirical force constant model derived from full inplane phonon dispersions of graphite [Mohr et al., Phys. Rev. B 76, 035439 (2007)] we calculate the tension coefficients of graphene. Extending the model by interplanar interactions, we calculate the elastic constants of graphite. The agreement of our theoretical values with inelastic x-ray scattering results on elastic constants of graphite [Bosak et al., Phys. Rev. B 75, 153408 (2007)] is very satisfactory.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Berlin	Editor
	Language		Wos	000260581800066	Publication Date	2008-08-25
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0370-1972;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	1.674	Times cited	47	Open Access
	Notes				Approved	Most recent IF: 1.674; 2008 IF: 1.166
	Call Number	UA @ lucian @ c:irua:75660			Serial	3621
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	Author	Michel, K.H.; Costamagna; Peeters, F.M.
	Title	Theory of thermal expansion in 2D crystals			Type	A1 Journal article
	Year	2015	Publication	Physica status solidi: B: basic research	Abbreviated Journal	Phys Status Solidi B
	Volume	252	Issue	252	Pages	2433-2437
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The thermal expansion alpha(T) in layered crystals is of fundamental and technological interest. As suggested by I. M. Lifshitz in 1952, in thin solid films (crystalline membranes) a negative contribution to alpha(T) is due to anharmonic couplings between in-plane stretching modes and out-of-plane bending (flexural modes). Genuine in-plane anharmonicities give a positive contribution to alpha(T). The competition between these two effects can lead to a change of sign (crossover) from a negative value of alpha(T) in a temperature (T) range T <= T-alpha to a positive value of alpha(T) for T > T-alpha in layered crystals. Here, we present an analytical lattice dynamical theory of these phenomena for a two-dimensional (2D) hexagonal crystal. We start from a Hamiltonian that comprises anharmonic terms of third and fourth order in the lattice displacements. The in-plane and out-of-plane contributions to the thermal expansion are studied as functions of T for crystals of different sizes. Besides, renormalization of the flexural mode frequencies plays a crucial role in determining the crossover temperature T-alpha. Numerical examples are given for graphene where the anharmonic couplings are determined from experiments. The theory is applicable to other layer crystals wherever the anharmonic couplings are known. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Berlin	Editor
	Language		Wos	000364690400014	Publication Date	2015-08-06
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0370-1972	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	1.674	Times cited	21	Open Access
	Notes	; We thank B. Verberck, D. Lamoen, and A. Dobry for useful comments. We acknowledge funding from the FWO (Belgium)-MINCyT (Argentina) collaborative research project. This work is supported by the Euro GRAPHENE project CONGRAN. ;			Approved	Most recent IF: 1.674; 2015 IF: 1.489
	Call Number	UA @ lucian @ c:irua:130281			Serial	4264
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	Author	Michel, K.H.; Neek-Amal, M.; Peeters, F.M.
	Title	Static flexural modes and piezoelectricity in 2D and layered crystals			Type	A1 Journal article
	Year	2016	Publication	Physica status solidi: B: basic research	Abbreviated Journal	Phys Status Solidi B
	Volume	253	Issue	253	Pages	2311-2315
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Piezo- and flexoelectricity are manifestations of electromechanical coupling in solids with potential applications in nanoscale materials. Naumov etal. [Phys. Rev. Lett. 102, 217601 (2009)] have shown by first principles calculations that a monolayer BN sheet becomes macroscopically polarized in-plane when in a corrugated state. Here, we investigate the interplay of layer corrugation and in-plane polarization by atomistic lattice dynamics. We treat the coupling between static flexural modes and in-plane atomic ion displacements as an anharmonic effect, similar to the membrane effect that is at the origin of negative thermal expansion in layered crystals. We have derived analytical expressions for the corrugation-induced static in-plane strains and the optical displacements with the resulting polarization response functions. Beyond h-BN, the theory applies to transition metal dichalcogenides and dioxides. Numerical calculations show that the effects are considerably stronger for 2D h-BN than for 2H-MoS2.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Berlin	Editor
	Language		Wos	000390339000002	Publication Date	2016-10-21
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0370-1972	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	1.674	Times cited	5	Open Access
	Notes	; The authors acknowledge useful discussions with L. Wirtz, A. Molina-Sanchez, and C. Sevik. This work was supported by the ESF-Eurographene project CONGRAN, and the Flemish Science Foundation (FWO-Vl). ;			Approved	Most recent IF: 1.674
	Call Number	UA @ lucian @ c:irua:140309			Serial	4462
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	Author	Michel, K.H.; Verberck, B.; Nikolaev, A.V.
	Title	Anisotropic packing and one-dimensional fluctuations of C₆₀ molecules in carbon nanotubes			Type	A1 Journal article
	Year	2005	Publication	Physical review letters	Abbreviated Journal	Phys Rev Lett
	Volume	95	Issue	18	Pages	185506-185506,4
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The confinement of a C-60 molecule encapsulated in a cylindrical nanotube depends on the tube radius. In small tubes with radius R-T less than or similar to 7 A, a fivefold axis of the molecule coincides with the tube axis. The interaction between C-60 molecules in the nanotube is then described by a O-2-rotor model on a 1D liquid chain with coupling between orientational and displacive correlations. This coupling leads to chain contraction. The structure factor of the 1D liquid is derived. In tubes with a larger radius the molecular centers of mass are displaced off the tube axis. The distinction of two groups of peapods with on- and off-axis molecules suggests an explanation of the apparent splitting of A(g) modes of C-60 in nanotubes measured by resonant Raman scattering.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York, N.Y.	Editor
	Language		Wos	000232887400041	Publication Date	2005-10-28
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0031-9007;1079-7114;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	8.462	Times cited	40	Open Access
	Notes				Approved	Most recent IF: 8.462; 2005 IF: 7.489
	Call Number	UA @ lucian @ c:irua:94717			Serial	127
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	Author	Bussmann-Holder, A.; Michel, K.H.
	Title	Bond geometry and phase transition mechanism of H-bonded ferroelectricity			Type	A1 Journal article
	Year	1998	Publication	Physical review letters	Abbreviated Journal	Phys Rev Lett
	Volume	80	Issue		Pages	2173-2176
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York, N.Y.	Editor
	Language		Wos	000072385400037	Publication Date	2002-07-27
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0031-9007;1079-7114;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	8.462	Times cited	81	Open Access
	Notes				Approved	Most recent IF: 8.462; 1998 IF: 6.017
	Call Number	UA @ lucian @ c:irua:23987			Serial	246
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	Author	Michel, K.H.; Copley, J.R.D.; Neumann, D.A.
	Title	Microscopic theory of orientational disorder and the orientational phase transition in solid C₆₀			Type	A1 Journal article
	Year	1992	Publication	Physical review letters	Abbreviated Journal	Phys Rev Lett
	Volume	68	Issue	19	Pages	2929-2932
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	We have developed a microscopic theory which describes the orientational dynamics of C60 molecules in the face-centered-cubic phase of C60 fullerite. The molecular interaction potential and the crystal-field potential are formulated in terms of symmetry-adapted rotator functions. The phase transition to the Pa3BAR structure is driven by an active multipolar mode of T2g symmetry belonging to the l = 10 manifold. The Birman criterion is satisfied. The transition is found to be of first order.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York, N.Y.	Editor
	Language		Wos	A1992HT64800019	Publication Date	2002-07-27
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0031-9007;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	7.512	Times cited	94	Open Access
	Notes				Approved
	Call Number	UA @ lucian @ c:irua:95492			Serial	2032
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	Author	Michel, K.H.; Nikolaev, A.V.
	Title	Theory of distinct crystal structures of polymerized fullerides AC₆₀, A=K, Rb, Cs: the specific role of alkalis			Type	A1 Journal article
	Year	2000	Publication	Physical review letters	Abbreviated Journal	Phys Rev Lett
	Volume	85	Issue		Pages	3197-3200
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York, N.Y.	Editor
	Language		Wos	000089807800033	Publication Date	2002-07-27
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0031-9007;1079-7114;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	8.462	Times cited	16	Open Access
	Notes				Approved	Most recent IF: 8.462; 2000 IF: 6.462
	Call Number	UA @ lucian @ c:irua:34339			Serial	3615
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	Author	Bostoen, C.; Michel, K.H.
	Title	Dynamics of a quadrupolar glass			Type	A1 Journal article
	Year	1991	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	43	Issue		Pages	4415-4422
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	A1991EX92100073	Publication Date	0000-00-00
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1098-0121; 0163-1829	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.736	Times cited	33	Open Access
	Notes				Approved	no
	Call Number	UA @ lucian @ c:irua:939			Serial	773
Permanent link to this record



	Author	Beheshtian, J.; Sadeghi, A.; Neek-Amal, M.; Michel, K.H.; Peeters, F.M.
	Title	Induced polarization and electronic properties of carbon-doped boron nitride nanoribbons			Type	A1 Journal article
	Year	2012	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	86	Issue	19	Pages	195433-195438
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The electronic properties of boron nitride nanoribbons (BNNRs) doped with a line of carbon atoms are investigated using density functional calculations. By replacing a line of alternating B and N atoms with carbons, three different configurations are possible depending on the type of the atoms which bond to the carbons. We found very different electronic properties for these configurations: (i) the NCB arrangement is strongly polarized with a large dipole moment having an unexpected direction, (ii) the BCB and NCN arrangements are nonpolar with zero dipole moment, (iii) the doping by a carbon line reduces the band gap regardless of the local arrangement of the borons and the nitrogens around the carbon line, and (iv) the polarization and energy gap of the carbon-doped BNNRs can be tuned by an electric field applied parallel to the carbon line. Similar effects were found when either an armchair or zigzag line of carbon was introduced.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000311694200006	Publication Date	2012-11-29
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1098-0121;1550-235X;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	41	Open Access
	Notes	; We would like to thank J. M. Pereira and S. Goedecker for helpful discussions. This work was supported by the Flemish Science Foundation (FWO-Vl), the ESF-EuroGRAPHENE project CONGRAN. M. N.-A is supported by EU-Marie Curie IIF postdoc Fellowship/299522. ;			Approved	Most recent IF: 3.836; 2012 IF: 3.767
	Call Number	UA @ lucian @ c:irua:105136			Serial	1603
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	Author	Tsvyashchenko, A.V.; Nikolaev, A.V.; Velichkov, A.I.; Salamatin, A.V.; Fomicheva, L.N.; Ryasny, G.K.; Sorokin, A.A.; Kochetov, O.I.; Budzynski, M.; Michel, K.H.
	Title	Lowering of the spatial symmetry at the gamma ->alpha phase transition in cerium			Type	A1 Journal article
	Year	2010	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	82	Issue	9	Pages	1-4
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Using time-differential perturbed angular correlation spectroscopy we have measured the electric field gradient (EFG) at 111Cd probe nuclei in solid Ce in a pressure range up to 8 GPa. Covering various allotropic phases of Ce, we find that the value of the EFG in the cubic α phase is almost four times larger than in the cubic γ phase and close to values in the noncubic phases α′ and α″. These results together with the differences in time modulation of the spectra are interpreted as evidence for quadrupolar electronic charge-density ordering and symmetry lowering at the γ→α transition while the lattice remains face-centered cubic
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000282004400001	Publication Date	2010-09-16
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1098-0121;1550-235X;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	11	Open Access
	Notes	; This work is supported by the Program of the Presidium of the Russian Academy of Sciences “Physics of Strongly Compressed Matter.” We are grateful to S. M. Stishov, B. Verberck, A. N. Grum-Grzhimailo, V. B. Brudanin and G. Heger for support of this work and discussion of the results. ;			Approved	Most recent IF: 3.836; 2010 IF: 3.774
	Call Number	UA @ lucian @ c:irua:85464			Serial	1854
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	Author	Zieliński, P.; Michel, K.H.
	Title	Microscopic model of surfaces in orientationally disordered ionic crystals : the (001) surface of KCN			Type	A1 Journal article
	Year	1992	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	46	Issue	8	Pages	4806-4815
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The crystallographic structure and the distribution of orientations of molecular ions are studied near the surface in an orientationally disordered crystal with the use of a Green-function formalism. The orientational degrees of freedom are treated by means of symmetry-adapted functions of angular coordinates. The structure of the (001) surface of KCN in its cubic fcc phase is then predicted using the existing data on the interaction of the ions K+ and CN-. A local antiferroelectric and antiferroelastic order i shown to exist in the surface region. The magnitude of the order and the spatial extent of the ordered re ion increase as the temperature approaches the point of the phase transition to the ordered phase. The,influence of the external electric field on the structure of the surface is predicted.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	A1992JK72500049	Publication Date	2002-07-27
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0163-1829;1095-3795;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.736	Times cited	4	Open Access
	Notes				Approved	PHYSICS, CONDENSED MATTER 16/67 Q1 #
	Call Number	UA @ lucian @ c:irua:2974			Serial	2029
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	Author	Callebaut, A.K.; Michel, K.H.
	Title	Microscopic theory of orientational disorder and lattice instability in solid C₇₀			Type	A1 Journal article
	Year	1995	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	52	Issue	21	Pages	15279-15290
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	We have developed a microscopic theory which describes the orientational dynamics of C-70 molecules and its coupling to lattice displacements in the face-centered-cubic phase of C-70 fullerite. The single-molecule orientational density distribution in the disordered phase is calculated. The ferroelastic transition to the rhombohedral phase is investigated. The discontinuity of the orientational order parameter at the phase transition is calculated. It is found that the transition leads to a stretching of the primitive unit cell along a [111] cubic direction. A softening of the elastic constant c(44) at the transition is predicted.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	A1995TK97900042	Publication Date	2002-07-27
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0163-1829;1095-3795;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.736	Times cited	20	Open Access
	Notes				Approved	PHYSICS, APPLIED 28/145 Q1 #
	Call Number	UA @ lucian @ c:irua:104421			Serial	2031
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	Author	Nikolaev, A.V.; Michel, K.H.
	Title	Microscopic theory of quadrupolar oredring in TmTe			Type	A1 Journal article
	Year	2001	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	63	Issue		Pages	1-10
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	000167402100025	Publication Date	2002-07-27
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0163-1829;1095-3795;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	7	Open Access
	Notes				Approved	Most recent IF: 3.836; 2001 IF: NA
	Call Number	UA @ lucian @ c:irua:36882			Serial	2033
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	Author	Nikolaev, A.V.; Michel, K.H.
	Title	Microscopic theory of the rhombohedral phase and transition to the monoclinic phase of solid C₇₀			Type	A1 Journal article
	Year	1996	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	54	Issue	18	Pages	12733-12743
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Starting from a model of microscopic interactions between C-70 molecules, we have developed a theory which describes the orientational dynamics and its coupling to lattice displacements in the rhombohedral phase of C-70 fullerite. The Landau free energy is calculated. We obtain a first-order phase transition to a monoclinic structure with the space group P2(1)/m. The transition is driven by the condensation of orientational quadrupoles at the F point of the Brillouin zone of the rhombohedral lattice. We find no evidence that the monoclinic structure is connected with the freezing in of orientations around the fivefold molecular axis. We calculate the lattice strains that are associated with the transition to the monoclinic structure. The theory is compared with a range of experimental data on the phase transition.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	A1996VT68200028	Publication Date	2002-07-27
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0163-1829;1095-3795;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.736	Times cited	5	Open Access
	Notes				Approved	no
	Call Number	UA @ lucian @ c:irua:16357			Serial	2034
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	Author	Lamoen, D.; Michel, K.H.
	Title	Microscopic theory of thermoelastic phenomena and pressure dependence in solid C₆₀			Type	A1 Journal article
	Year	1993	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	48	Issue	2	Pages	807-813
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	A microscopic theory for the coupling of molecular orientations with acoustic lattice displacements is proposed. The relevant interaction is quadratic in the orientational-order-parameter variables and linear in longitudinal strains. The coupling is evaluated for a complex molecular structure. The intermolecular potential is obtained from interaction centers placed at nuclei and at the centers of interatomic bonds. The free energy is derived and the experimental consequences of the theory are studied. The Clausius-Clapeyron equation for orientational melting is obtained. The theory explains the decrease of the lattice constant at the first-order phase transition and the increase of the transition temperature with applied pressure.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	A1993LM88500014	Publication Date	2002-07-27
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0163-1829;1095-3795;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.736	Times cited	32	Open Access
	Notes				Approved	PHYSICS, CONDENSED MATTER 16/67 Q1 #
	Call Number	UA @ lucian @ c:irua:5779			Serial	2035
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	Author	Verberck, B.; Michel, K.H.
	Title	Nanotube field and orientational properties of C₇₀ molecules in carbon nanotubes			Type	A1 Journal article
	Year	2007	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	75	Issue	4	Pages	045419,1-14
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The orientation of a C(70) fullerene molecule encapsulated in a single-walled carbon nanotube (SWCNT) depends on the tube radius. First we confirm that chirality effects do not affect the orientation as well by comparing discrete atomistic calculations with the results of a continuous tube approximation for a variety of SWCNTs. The molecular and the tube symmetry are exploited by using symmetry-adapted rotator functions. We accurately determine the optimal molecular orientation as a function of the tube radius; for low (less than or similar to 7 A) and high (greater than or similar to 7.2 A) tube radii, lying and standing molecular orientations are recovered, respectively. In between, we observe a transition regime. In addition, we consider off-axis positions. We perform a one-dimensional liquid description of a chain of on-axis C(70) molecules inside a SWCNT. All results agree well with recent x-ray diffraction experiments.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	000243895600128	Publication Date	2007-01-17
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1098-0121;1550-235X;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	23	Open Access
	Notes				Approved	Most recent IF: 3.836; 2007 IF: 3.172
	Call Number	UA @ lucian @ c:irua:63752			Serial	2280
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	Author	Verberck, B.; Michel, K.H.
	Title	Nanotube field of C₆₀ molecules in carbon nanotubes: atomistic versus continuous approach			Type	A1 Journal article
	Year	2006	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	74	Issue	4	Pages	045421,1-14
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	000239426800113	Publication Date	2006-07-22
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1098-0121;1550-235X;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	31	Open Access
	Notes				Approved	Most recent IF: 3.836; 2006 IF: 3.107
	Call Number	UA @ lucian @ c:irua:60090			Serial	2281
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	Author	Verberck, B.; Nikolaev, A.V.; Michel, K.H.
	Title	Orientational charge density waves and the metal-insulator transition in polymerized KC₆₀			Type	A1 Journal article
	Year	2005	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	71	Issue	16	Pages	165117-11
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	A theoretical model is presented for the description of the metal-insulator transition which accompanies the structural phase transition at T approximate to 50 K in polymerized KC60. The model involves orientational charge density waves (along the C-60 polymer chains) which were introduced previously for a description of the structural phase transition. A satisfactory qualitative and quantitative understanding is obtained when the three-dimensionality of the crystal and the presence of the K+ counterions is properly taken into account.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000228763100035	Publication Date	2005-04-27
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1098-0121;1550-235X;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	1	Open Access
	Notes				Approved	Most recent IF: 3.836; 2005 IF: 3.185
	Call Number	UA @ lucian @ c:irua:104076			Serial	2514
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	Author	Michel, K.H.; Verberck, B.
	Title	Phonon dispersions and piezoelectricity in bulk and multilayers of hexagonal boron nitride			Type	A1 Journal article
	Year	2011	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	83	Issue	11	Pages	115328-115328,14
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	A unified theory of phonon dispersions and piezoelectricity in bulk and multilayers of hexagonal boron nitride (h-BN) is derived. The dynamical matrix is calculated on the basis of an empirical force constant model of intralayer valence and interlayer van der Waals interactions. Coulomb interactions are calculated by Ewalds method, adapted for the three-dimensional (3D) and the multilayer case. The deformation of the ionic charge distribution with long-wave lattice displacements is taken into account. Special attention is devoted to the nonanalytic long-range Coulomb contribution to the dynamical matrix which is different for the 3D crystal and the multilayer case. Consequently there is a splitting of the transverse optical (TO) and longitudinal optical (LO) phonon branches of E1u symmetry and a discontinuity of the A2u branch at the Γ point in 3D h-BN. No such splitting and discontinuity at Γ are present in multilayer crystals with a finite number N of layers. There a diverging bundle of N overbending optical phonon branches emerges from Γ. Borns long-wave theory is applied and extended for the study of piezoelectricity in layered crystals. While 3D h-BN and h-BN multilayers with an even number of layers (symmetry D6h) are not piezoelectric, multilayers with an uneven number of Nu layers (symmetry D3h) are piezoelectric; the piezoelectric coefficient e1,11 is inversely proportional to Nu.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000288783700005	Publication Date	2011-03-24
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1098-0121;1550-235X;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	82	Open Access
	Notes	; Discussions with G. Heger, B. Partoens, and F. M. Peeters are gratefully acknowledged. This work has been supported by the Flemish Science Foundation (FWO-V1) and the Bijzonder Onderzoeksfonds, Universiteit Antwerpen (BOF-UA). ;			Approved	Most recent IF: 3.836; 2011 IF: 3.691
	Call Number	UA @ lucian @ c:irua:89602			Serial	2603
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	Author	Nikolaev, A.V.; Michel, K.H.
	Title	Symmetry lowering at the structural phase transitions in NpO₂ and UO₂			Type	A1 Journal article
	Year	2003	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	68	Issue	5	Pages	054112-054112,7
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The structural phase transitions with electric-quadrupole long-range order in NpO2 (Fm (3) over barm-->Pn (3) over barm) and UO2 (Fm (3) over barm-->Pa (3) over bar) are analyzed from a group theoretical point of view. In both cases, the symmetry lowering involves three quadrupolar components belonging to the irreducible representation T-2g (Gamma(5)) of O-h and condensing in a triple-q structure at the X point of the Brillouin zone. The Pa (3) over bar structure is close to Pn (3) over barm, but allows for oxygen displacements. The Pa (3) over bar ordering leads to an effective electrostatic attraction between electronic quadrupoles while the Pn (3) over barm ordering results in a repulsion between them. It is concluded that the Pn (3) over barm structure can be stabilized only through some additional process such as strengthening of the chemical bonding between Np and O. We also derive the relevant structure-factor amplitudes for Pn (3) over barm and Pa (3) over bar, and the effect of domains on resonant x-ray scattering experiments.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000185240100038	Publication Date	2003-08-29
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0163-1829;1095-3795;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	15	Open Access
	Notes				Approved	Most recent IF: 3.836; 2003 IF: NA
	Call Number	UA @ lucian @ c:irua:94847			Serial	3405
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	Author	Verberck, B.; Nikolaev, A.V.; Michel, K.H.
	Title	Theoretical model for the structural phase transition at the metal-insulator transition in polymerized KC₆₀			Type	A1 Journal article
	Year	2002	Publication	Physical Review B	Abbreviated Journal	Phys Rev B
	Volume	66	Issue	16	Pages	165425-165425,14
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The recently discovered structural transition in polymerized KC60 at about 50 K results in a doubling of the unit cell volume and accompanies the metal-insulator transition. Here we show that the ((a) over right arrow+(c) over right arrow,(b) over right arrow,(a) over right arrow-(c) over right arrow) superstructure results from small orientational charge density waves along the polymer chains and concomitant displacements of the surrounding K+ ions. The effect is specific for the space group Pmnn of KC60 and is absent in RbC60 and CsC60 (space group I2/m). The mechanism is relevant for the metal-insulator transition.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000179286400135	Publication Date	2002-10-30
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0163-1829;1095-3795;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	10	Open Access
	Notes				Approved	Most recent IF: 3.836; 2002 IF: NA
	Call Number	UA @ lucian @ c:irua:94907			Serial	3608
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	Author	Michel, K.H.; Verberck, B.
	Title	Theory of elastic and piezoelectric effects in two-dimensional hexagonal boron nitride			Type	A1 Journal article
	Year	2009	Publication	Physical review : B : solid state	Abbreviated Journal	Phys Rev B
	Volume	80	Issue	22	Pages	224301,1-224301,10
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	Starting from an empirical force constant model of valence interactions and calculating by Ewalds method the ion-ion force constants, we derive the dynamical matrix for a monolayer crystal of hexagonal boron nitride (h-BN). The phonon dispersion relations are calculated. The interplay between valence and Coulomb forces is discussed. It is shown by analytical methods that the longitudinal and the transverse optical (LO and TO) phonon branches for in-plane motion are degenerate at the Γ point of the Brillouin zone. Away from Γ, the LO branch exhibits pronounced overbending. It is found that the nonanalytic Coulomb contribution to the dynamical matrix causes a linear increase of the LO branch with increasing wave vector starting at Γ. This effect is general for two-dimensional (2D) ionic crystals. Performing a long-wavelength expansion of the dynamical matrix, we use Borns perturbation method to calculate the elastic constants (tension coefficients). Since the crystal is noncentrosymmetric, internal displacements due to relative shifts between the two sublattices (B and N) contribute to the elastic constants. These internal displacements are responsible for piezoelectric and dielectric phenomena. The piezoelectric stress constant and the dielectric susceptibility of 2D h-BN are calculated.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	000273228500045	Publication Date	2009-12-21
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1098-0121;1550-235X;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	96	Open Access
	Notes				Approved	Most recent IF: 3.836; 2009 IF: 3.475
	Call Number	UA @ lucian @ c:irua:80576			Serial	3616
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	Author	Michel, K.H.; Verberck, B.
	Title	Theory of rigid-plane phonon modes in layered crystals			Type	A1 Journal article
	Year	2012	Publication	Physical review : B : condensed matter and materials physics	Abbreviated Journal	Phys Rev B
	Volume	85	Issue	9	Pages	094303-094303,11
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	The lattice dynamics of low-frequency rigid-plane modes in metallic (graphene multilayers, GML) and in insulating (hexagonal boron-nitride multilayers, BNML) layered crystals is investigated. The frequencies of shearing and compression (stretching) modes depend on the layer number N and are presented in the form of fan diagrams. The results for GML and BNML are very similar. In both cases, only the interactions (van der Waals and Coulomb) between nearest-neighbor planes are effective, while the interactions between more distant planes are screened. A comparison with recent Raman scattering results on low-frequency shear modes in GML [Tan et al., Nat. Mater., in press, doi: 10.1038/nmat3245, (2012)] is made. Relations with the low-lying rigid-plane phonon dispersions in the bulk materials are established. Master curves, which connect the fan diagram frequencies for any given N, are derived. Static and dynamic thermal correlation functions for rigid-layer shear and compression modes are calculated. The results might be of use for the interpretation of friction force experiments on multilayer crystals.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000301646000006	Publication Date	2012-03-19
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1098-0121;1550-235X;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	3.836	Times cited	38	Open Access
	Notes	; The authors are indebted to J. Maultzsch for bringing Ref. 20 to their attention. They thank D. Lamoen, F.M. Peeters, B. Trauzettel, and C. Van Haesendonck for useful discussions. This work has been financially supported by the Research Foundation Flanders (FWO). ;			Approved	Most recent IF: 3.836; 2012 IF: 3.767
	Call Number	UA @ lucian @ c:irua:97787			Serial	3619
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