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	Author	Verberck, B.; Nikolaev, A.V.; Michel, K.H.
	Title	Theoretical model for the structural phase transition and the metal-insulator transition in polymerized KC₆₀			Type	A1 Journal article
	Year	2004	Publication	Fullerenes, nanotubes, and carbon nanostructures T2 – 6th Biennial International Workshop on Fullerenes and Atomic Clusters, JUN 30-JUL 04, 2003, St Petersburg, RUSSIA	Abbreviated Journal	Fuller Nanotub Car N
	Volume	12	Issue	1-2	Pages	243-252
	Keywords	A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
	Abstract	The recently discovered structural phase transition in Polymerized KC60 at about 50K leads to a doubling of the unit cell volume and is accompanied by a 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 orientational charge density waves along the polymer chains and correlated displacements of the K+ ions. The presented model can also account for the metal-insulator transition. The effect is specific for the space group Pmnn of KC60 and is absent in both Rb- and CsC60 (space group 12/m), in agreement with the present experimental knowledge of these compounds.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000220551600040	Publication Date	2004-03-15
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1536-383X;1536-4046;	ISBN		Additional Links	UA library record; WoS full record
	Impact Factor	1.35	Times cited		Open Access
	Notes				Approved	Most recent IF: 1.35; 2004 IF: 1.117
	Call Number	UA @ lucian @ c:irua:103259			Serial	3607
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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	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	Nikolaev, A.V.; Michel, K.H.
	Title	Ab initio approach to superexchange interactions in alkali doped fullerides AC₆₀			Type	P1 Proceeding
	Year	2004	Publication	AIP conference proceedings T2 – 18th International Winterschool/Euroconference on Electronic Properties, of Novel Materials, MAR 06-JUN 13, 2004, Kirchberg, AUSTRIA	Abbreviated Journal
	Volume		Issue		Pages	393-396
	Keywords	P1 Proceeding; Condensed Matter Theory (CMT)
	Abstract	The superexchange interactions between the fullerenes arise as a result of the electron transfer from the C-60 molecule to the alkali atom and back. We present a scheme, which is a configuration interaction approach based on the valence bond (Heitler-London) method. The effect of superexchange is described together with chemical bonding by constructing and solving a secular equation, rather than by using a perturbation treatment. We have considered 180degrees and 90degrees superexchange for the C-60 Cs-C-60 pathways. The calculations account for unusual electronic properties of polymer orthorhombic and quenched cubic phases of CsC60: two lines in nuclear magnetic resonance experiments, the development of a spin-singlet ground state and a decrease of magnetic susceptibility as T-->0.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York	Editor
	Language		Wos	000224699400085	Publication Date	2004-11-11
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume	723	Series Issue		Edition
	ISSN	0-7354-0204-3	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor		Times cited		Open Access
	Notes				Approved	Most recent IF: NA
	Call Number	UA @ lucian @ c:irua:103752			Serial	27
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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	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	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	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	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	Nikolaev, A.V.; Michel, K.H.
	Title	Molecular terms and optical transitions of C₆₀^n+/- molecular ions			Type	P1 Proceeding
	Year	2002	Publication	AIP conference proceedings T2 – 16th International Winterschool on Electronic Properties of Novel, Materials, MAR 02-09, 2002, KIRCHBERG, AUSTRIA	Abbreviated Journal
	Volume		Issue		Pages	417-420
	Keywords	P1 Proceeding; Condensed Matter Theory (CMT)
	Abstract	We have studied the molecular energy terms of the hole configurations (h(u)(+))(m), m=2,3,4,5 of C-60(m+) cations and the electronic configurations (t(1u))(n) n=2,3,4, as well as (t(1u))(n-1)t(1g) of the C-60(n-) anions. The lowest terms (within an energy span of 0.03 eV) for C-60(2+) are three triplets T-3(1g), (3)G(g), T-3(2g) and for C-60(3+) are three quartets T-4(1u), (4)G(u), T-4(2u), which favor Jahn-Teller distortions. For the ground state of C-60(2-) we find a triplet T-3(1g) in agreement with Hund's rules. Our method takes into account intramolecular direct and exchange multipolar Coulomb interactions.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	New York	Editor
	Language		Wos		Publication Date	0000-00-00
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume	633	Series Issue		Edition
	ISSN	0-7354-0088-1	ISBN		Additional Links	UA library record; WoS full record;
	Impact Factor		Times cited		Open Access
	Notes				Approved	Most recent IF: NA
	Call Number	UA @ lucian @ c:irua:103905			Serial	2187
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	Author	Michel, K.H.; Verberck, B.
	Title	Theory of the evolution of phonon spectra and elastic constants from graphene to graphite			Type	A1 Journal article
	Year	2008	Publication	Physical review : B : solid state	Abbreviated Journal	Phys Rev B
	Volume	78	Issue	8	Pages	085424,1-085424,17
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	We present a unified theory of the phonon dispersions and elastic properties of graphene, graphite, and graphene multilayer systems. Starting from a fifth-nearest-neighbor force-constant model derived from full in-plane phonon dispersions of graphite [Mohr et al., Phys. Rev. B 76, 035439 (2007)], we use Born's long-wave method to calculate the tension and bending coefficients of graphene. Extending the model by interplanar interactions, we study the phonon dispersions and the elastic constants of graphite, and the phonon spectra of graphene multilayers. We find that the inner displacement terms due to sublattice shifts between inequivalent C atoms are quantitatively important in determining the elastomechanical properties of graphene and of graphite. The overall agreement between theory and experiment is very satisfactory. We investigate the evolution from graphene to graphite by studying the increase in the rigid plane optical mode as a function of the number of layers N. At N=10 the graphite value B2g1127 cm−1 is attained within a few percent.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication	Lancaster, Pa	Editor
	Language		Wos	000259406900106	Publication Date	2008-08-21
	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	72	Open Access
	Notes				Approved	Most recent IF: 3.836; 2008 IF: 3.322
	Call Number	UA @ lucian @ c:irua:76527			Serial	3622
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	Author	Verberck, B.; Heresanu, V.; Rouziere, S.; Cambedouzou, J.; Launois, P.; Kovats, E.; Pekker, S.; Vliegenthart, G.A.; Michel, K.H.; Gompper, G.
	Title	Fullerene-cubane : X-ray scattering experiments and Monte Carlo simulations			Type	A1 Journal article
	Year	2008	Publication	Fullerenes, nanotubes, and carbon nanostructures T2 – 8th Biennial International Workshop on Fullerenes and Atomic Clusters, (IWFAC 2007), JUL 02-06, 2007, St Petersburg, RUSSIA	Abbreviated Journal	Fuller Nanotub Car N
	Volume	16	Issue	5-6	Pages	293-300
	Keywords	A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
	Abstract	We report single-crystal X-ray diffuse scattering measurements on C-60.C8H8 fullerene-cubane showing that the C-60 molecules are orientationally disordered at 300 and 150K and get ordered at low temperatures. Monte Carlo simulations provide further insight in the orientational behavior of both C-60 and C8H8 molecules; low-temperature molecular orientations are predicted.
	Address
	Corporate Author				Thesis
	Publisher		Place of Publication		Editor
	Language		Wos	000259645200003	Publication Date	2008-09-28
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	1536-383X;1536-4046;	ISBN		Additional Links	UA library record; WoS full record; WoS citing articles
	Impact Factor	1.35	Times cited	6	Open Access
	Notes				Approved	Most recent IF: 1.35; 2008 IF: 0.680
	Call Number	UA @ lucian @ c:irua:102640			Serial	1295
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	Author	Michel, K.H.; Verberck, B.; Nikolaev, A.
	Title	Mercator maps of orientations of a C₆₀ molecule in single-walled nanotubes with distinct radii			Type	A1 Journal article
	Year	2005	Publication	AIP conference proceedings	Abbreviated Journal
	Volume	786	Issue		Pages	69-72
	Keywords	A1 Journal article; Condensed Matter Theory (CMT)
	Abstract	We study the confinement of a C-60 molecule encapsulated in a cylindrical nanotube as a function of the tube radius. Drawing the Mercator maps of the potential, we find two distinct molecular orientations; for tubes with small radii, R-T less than or similar to 7 angstrom, a fivefold axis of the molecule coincides with the tube long axis, for larger radii, R-T less than or similar to 8 angstrom, a threefold axis of the molecule coincides with the tube long axis. These different orientations are caused by the relative importance of the repulsive and the attractive parts of the van der Waals potentials of the molecule with the tube wall for small and large tubes respectively. Experimental evidence is provided by the apparent splitting of A(g) modes of the C-60 molecule in resonant Raman scattering.
	Address
	Corporate Author				Thesis
	Publisher	Amer inst physics	Place of Publication	Melville	Editor
	Language		Wos		Publication Date	0000-00-00
	Series Editor		Series Title		Abbreviated Series Title
	Series Volume		Series Issue		Edition
	ISSN	0094-243x	ISBN		Additional Links	UA library record; WoS full record;
	Impact Factor		Times cited		Open Access
	Notes				Approved	Most recent IF: NA
	Call Number	UA @ lucian @ c:irua:94738			Serial	1993
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