“Coupling of orientational and translational modes in solid C60 and C70”. Lamoen D, Michel KH, Phase transitions 67, 789 (1999). http://doi.org/10.1080/01411599908224511
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.06
Times cited: 2
DOI: 10.1080/01411599908224511
|
“Quantum charge density fluctuations and the γ-&alpha, phase transition in Ce”. Nikolaev AV, Michel KH, European physical journal : B : condensed matter and complex systems 9, 619 (1999). http://doi.org/10.1007/s100510050806
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.461
Times cited: 19
DOI: 10.1007/s100510050806
|
“Orientational disorder and order in C60-fullerite and in MC60-alkali metal fullerides”. Nikolaev AV, Michel KH, Copley JRD Plenum Press, New York, page 183 (1999).
Keywords: H3 Book chapter; Condensed Matter Theory (CMT)
|
“Free energy and orientational phase transition in solid C60”. Michel KH, Zeitschrift für Physik: B 88, 71 (1992). http://doi.org/10.1007/BF01573839
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Times cited: 33
DOI: 10.1007/BF01573839
|
“Sequence of orientational phase transitions in solid C60”. Michel KH, Chemical physics letters 193, 478 (1992). http://doi.org/10.1016/0009-2614(92)85835-X
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.897
Times cited: 14
DOI: 10.1016/0009-2614(92)85835-X
|
“Molecular structure and orientational ordering in solid C60”. Michel KH, The journal of chemical physics 97, 5155 (1992). http://doi.org/10.1063/1.463813
Abstract: A microscopic theory, which describes the orientational dynamics of C60 molecules in the face-centered cubic phase of C60-fullerite, is formulated or the case of a complex molecular structure. Interaction centers which comprise atoms, double bonds, and single bonds as molecular constituents contribute to the intermolecular potential. Orientation dependent physical properties are described in terms of symmetry-adapted rotator functions. It is found that a same set of rotator functions is sufficient even in the case of a complex molecular structure. Phase transition temperatures are discussed for various models of molecular structure.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.952
Times cited: 20
DOI: 10.1063/1.463813
|
“Microscopic model of surfaces in orientationally disordered ionic crystals : the (001) surface of KCN”. Zieliński P, Michel KH, Physical review : B : condensed matter and materials physics 46, 4806 (1992). http://doi.org/10.1103/PhysRevB.46.4806
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.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.736
Times cited: 4
DOI: 10.1103/PhysRevB.46.4806
|
“Electric quadrupole interactions and the γ-&alpha, phase transition in Ce: the role of conduction electrons”. Nikolaev AV, Michel KH, European physical journal : B : condensed matter and complex systems 17, 15 (2000). http://doi.org/10.1007/s100510070156
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.461
Times cited: 8
DOI: 10.1007/s100510070156
|
“Theory of distinct crystal structures of polymerized fullerides AC60, A=K, Rb, Cs: the specific role of alkalis”. Michel KH, Nikolaev AV, Physical review letters 85, 3197 (2000). http://doi.org/10.1103/PhysRevLett.85.3197
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 8.462
Times cited: 16
DOI: 10.1103/PhysRevLett.85.3197
|
“Electronic structure and electric quadrupoles of a polymerized chain in solid AC60”. Nikolaev AV, Michel KH, Solid state communications 117, 739 (2001). http://doi.org/10.1016/S0038-1098(01)00017-5
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.554
Times cited: 10
DOI: 10.1016/S0038-1098(01)00017-5
|
“Microscopic theory of quadrupolar oredring in TmTe”. Nikolaev AV, Michel KH, Physical review : B : condensed matter and materials physics 63, 1 (2001). http://doi.org/10.1103/PhysRevB.63.104105
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 7
DOI: 10.1103/PhysRevB.63.104105
|
“Theory of crystal structures of polymerized C60-fullerite and fullerides AC60, A=K, Rb, Cs”. Michel KH, Nikolaev AV, Verberck B s.l. (2001).
Keywords: H1 Book chapter; Condensed Matter Theory (CMT)
|
“Free energy and structural phase transitions in mixed crystals: a microscopic derivation”. Theuns T, Michel KH, Zeitschrift für Physik: B 86, 125 (1992). http://doi.org/10.1007/BF01323556
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Times cited: 1
DOI: 10.1007/BF01323556
|
“Nanotube field and one-dimensional fluctuations of C60 molecules in carbon nanotubes”. Michel KH, Verberck B, Nikolaev AV, European physical journal : B : condensed matter and complex systems 48, 113 (2005). http://doi.org/10.1140/epjb/e2005-00378-9
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.461
Times cited: 25
DOI: 10.1140/epjb/e2005-00378-9
|
“Crystal field and molecular structure of solid C60”. Lamoen D, Michel KH, Zeitschrift für Physik : B : condensed matter 92, 323 (1993). http://doi.org/10.1007/BF01308749
Abstract: The crystal field in the orientationally disordered phase of C90-fullerite is derived from an intermolecular potential model, which takes into account the geometric difference between double bonds and single bonds. The molecules are modelled as rigid bodies, atoms and single bonds are treated as single interaction centers, while double bonds are described by a distribution of interaction centers along the bond. The crystal field is expanded in terms of cubic rotator functions. The calculated expansion coefficients are compared with empirical values derived from diffraction data. The angular dependence of the crystal field, resulting from an anticlockwise rotation of the molecule around the [111] axis, exhibits an absolute and a secondary minimum at angles of 98-degrees and 38-degrees respectively. The self interaction of the molecule in a deformable lattice is investigated.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Times cited: 25
DOI: 10.1007/BF01308749
|
“Neutron and X-ray scattering cross sections of orientationally disordered solid C60”. Copley JRD, Michel KH, Journal Of Physics-Condensed Matter 5, 4353 (1993)
Keywords: A1 Journal article; Electron Microscopy for Materials Science (EMAT);
Impact Factor: 2.346
Times cited: 34
|
“Microscopic theory of thermoelastic phenomena and pressure dependence in solid C60”. Lamoen D, Michel KH, Physical review : B : condensed matter and materials physics 48, 807 (1993). http://doi.org/10.1103/PhysRevB.48.807
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.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.736
Times cited: 32
DOI: 10.1103/PhysRevB.48.807
|
“The C60 molecules in (C60)N@SWCNT peapods: crystal field, intermolecular interactions and dynamics”. Verberck B, Michel KH, Nikolaev AV, Fullerenes, nanotubes, and carbon nanostructures 14, 171 (2006). http://doi.org/10.1080/15363830600663529
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.35
Times cited: 10
DOI: 10.1080/15363830600663529
|
“Nanotube field of C60 molecules in carbon nanotubes: atomistic versus continuous approach”. Verberck B, Michel KH, Physical review : B : condensed matter and materials physics 74, 045421 (2006). http://doi.org/10.1103/PhysRevB.74.045421
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 31
DOI: 10.1103/PhysRevB.74.045421
|
“Superposition of quantum and classical rotational motions in Sc2C2@C84 fullerite”. Michel KH, Verberck B, Hulman M, Kuzmany H, Krause M, The journal of chemical physics 126, 064304 (2007). http://doi.org/10.1063/1.2434175
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.965
Times cited: 14
DOI: 10.1063/1.2434175
|
“Nanotube field and orientational properties of C70 molecules in carbon nanotubes”. Verberck B, Michel KH, Physical review : B : condensed matter and materials physics 75, 045419 (2007). http://doi.org/10.1103/PhysRevB.75.045419
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.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 23
DOI: 10.1103/PhysRevB.75.045419
|
“Nanotube field of C60 and C70 molecules in carbon nanotubes”. Verberck B, Michel KH, International journal of quantum chemistry 107, 2294 (2007). http://doi.org/10.1002/qua.21309
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.92
Times cited: 6
DOI: 10.1002/qua.21309
|
“Anisotropic packing of C-70 molecules in carbon nanotubes”. Verberck B, Michel KH, Physica status solidi B-basic solid state physics 244, 4279 (2007). http://doi.org/10.1002/pssb.200776144
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.674
DOI: 10.1002/pssb.200776144
|
“Theory of the elastic constants of graphite and graphene”. Michel KH, Verberck B, Physica status solidi: B: basic research 245, 2177 (2008). http://doi.org/10.1002/pssb.200879604
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.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.674
Times cited: 47
DOI: 10.1002/pssb.200879604
|
“Theory of the evolution of phonon spectra and elastic constants from graphene to graphite”. Michel KH, Verberck B, Physical review : B : solid state 78, 085424 (2008). http://doi.org/10.1103/PhysRevB.78.085424
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.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 72
DOI: 10.1103/PhysRevB.78.085424
|
“Elusive s-f intrasite interactions and double exchange in solids: ferromagnetic versus nonmagnetic ground state”. Nikolaev AV, Michel KH, Journal of experimental and theoretical physics 109, 286 (2009). http://doi.org/10.1134/S1063776109080147
Abstract: From the theory of many-electron states in atoms, we know that there exists a strong Coulomb repulsion, which results in the electronic term structure of atoms and is responsible for Hunds rules. By expanding the Coulomb on-site repulsion into a multipolar series, we derive this interaction and show that it is also present in solids as a correlation effect, which means that the interaction requires a multideterminant version of the Hartree-Fock method. Of particular interest is the case where this interaction couples states of localized ( f) and delocalized ( s) electrons. We show that the interaction is bilinear in the creation/annihilation operators for localized electrons and bilinear in the operators for conduction electrons. To study the coupling, we consider a simple model in the framework of an effective limited configuration interaction method with one localized f-electron and one itinerant s-electron per crystal site. The on-site multipole interaction between the f- and s-electrons is explicitly taken into account. It is shown that depending on the low-lying excitation spectrum imposed by the crystal electric field, the model can lead not only to ferromagnetism but also to a nonmagnetic state. The model is relevant for solids with localized and itinerant electron states.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.196
Times cited: 3
DOI: 10.1134/S1063776109080147
|
“Theory of elastic and piezoelectric effects in two-dimensional hexagonal boron nitride”. Michel KH, Verberck B, Physical review : B : solid state 80, 224301 (2009). http://doi.org/10.1103/PhysRevB.80.224301
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.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 96
DOI: 10.1103/PhysRevB.80.224301
|
“Theoretical phonon dispersions in monolayers and multilayers of hexagonal boron-nitride”. Michel KH, Verberck B, Physica status solidi: B: basic research 246, 2802 (2009). http://doi.org/10.1002/pssb.200982307
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.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.674
Times cited: 10
DOI: 10.1002/pssb.200982307
|
“Lowering of the spatial symmetry at the gamma ->alpha phase transition in cerium”. Tsvyashchenko AV, Nikolaev AV, Velichkov AI, Salamatin AV, Fomicheva LN, Ryasny GK, Sorokin AA, Kochetov OI, Budzynski M, Michel KH, Physical review : B : condensed matter and materials physics 82, 1 (2010). http://doi.org/10.1103/PhysRevB.82.092102
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
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 11
DOI: 10.1103/PhysRevB.82.092102
|
“Phonon dispersions and piezoelectricity in bulk and multilayers of hexagonal boron nitride”. Michel KH, Verberck B, Physical review : B : condensed matter and materials physics 83, 115328 (2011). http://doi.org/10.1103/PhysRevB.83.115328
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.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 82
DOI: 10.1103/PhysRevB.83.115328
|