31 research outputs found
Superconductivity near the vibrational mode instability in MgCNi3
To understand the role of electron-phonon interaction in superconducting
MgCNi we have performed density functional based linear response
calculations of its lattice dynamical properties. A large coupling constant = 1.51 is predicted and contributing phonons are identified as
displacements of Ni atoms towards octahedral interstitials of the perovskite
lattice. Instabilities found for some vibrational modes emphasize the role of
anharmonic effects in resolving experimental controversies.Comment: 4 pages, 4 eps figures, replaces the older versio
Dimensional trend in CePt2In7, Ce-115 compounds, and CeIn3
We present realistic Kondo-lattice simulation results for the
recently-discovered heavy-fermion antiferromagnet CePt2In7 comparing with its
three-dimensional counterpart CeIn3 and the less two-dimensional ones,
Ce-115's. We find that the distance to the magnetic quantum critical point is
the largest for CeIn3 and the smallest for Ce-115's, and CePt2In7 falls in
between. We argue that the trend in quasi-two-dimensional materials stems from
the frequency dependence of the hybridization between Cerium 4f-electrons and
the conduction bands.Comment: 4.8 pages, 5 figure
Linear-response theory and lattice dynamics: a muffin-tin orbital approach
A detailed description of a method for calculating static linear-response
functions in the problem of lattice dynamics is presented. The method is based
on density functional theory and it uses linear muffin-tin orbitals as a basis
for representing first-order corrections to the one-electron wave functions. As
an application we calculate phonon dispersions in Si and NbC and find good
agreement with experiments.Comment: 18 pages, Revtex, 2 ps figures, uuencoded, gzip'ed, tar'ed fil
Acoustical-Mode-Driven Electron-Phonon Coupling in Transition-Metal Diborides
We show that the electron-phonon coupling in the transition-metal diborides
NbB2 and TaB2 is dominated by the longitudinal acoustical (LA) mode, in
contrast to the optical E_{2g} mode dominated coupling in MgB2. Our ab initio
results, described in terms of phonon dispersion, linewidth, and partial
electron-phonon coupling along Gamma to A, also show that (i) NbB2 and TaB2
have a relatively weak electron-phonon coupling, (ii) the E_{2g} linewidth is
an order of magnitude larger in MgB2 than in NbB2 or TaB2, (iii) the E_{2g}
frequency in NbB2 and TaB2 is considerably higher than in MgB2, and (iv) the LA
frequency at A for TaB2 is almost half of that of MgB2 or NbB2.Comment: 4 pages, 4 figures, and 1 tabl
Ab initio calculations of the physical properties of transition metal carbides and nitrides and possible routes to high-Tc
Ab initio linear-response calculations are reported of the phonon spectra and
the electron-phonon interaction for several transition metal carbides and
nitrides in a NaCl-type structure. For NbC, the kinetic, optical, and
superconducting properties are calculated in detail at various pressures and
the normal-pressure results are found to well agree with the experiment.
Factors accounting for the relatively low critical temperatures Tc in
transition metal compounds with light elements are considered and the possible
ways of increasing Tc are discussed.Comment: 19 pages, 7 figure
First- principle calculations of magnetic interactions in correlated systems
We present a novel approach to calculate the effective exchange interaction
parameters based on the realistic electronic structure of correlated magnetic
crystals in local approach with the frequency dependent self energy. The analog
of ``local force theorem'' in the density functional theory is proven for
highly correlated systems. The expressions for effective exchange parameters,
Dzialoshinskii- Moriya interaction, and magnetic anisotropy are derived. The
first-principle calculations of magnetic excitation spectrum for ferromagnetic
iron, with the local correlation effects from the numerically exact QMC-scheme
is presented.Comment: 17 pages, 3 Postscript figure
Phonons and related properties of extended systems from density-functional perturbation theory
This article reviews the current status of lattice-dynamical calculations in
crystals, using density-functional perturbation theory, with emphasis on the
plane-wave pseudo-potential method. Several specialized topics are treated,
including the implementation for metals, the calculation of the response to
macroscopic electric fields and their relevance to long wave-length vibrations
in polar materials, the response to strain deformations, and higher-order
responses. The success of this methodology is demonstrated with a number of
applications existing in the literature.Comment: 52 pages, 14 figures, submitted to Review of Modern Physic
Semiempirical Hartree-Fock calculations for KNbO3
In applying the semiempirical intermediate neglect of differential overlap
(INDO) method based on the Hartree-Fock formalism to a cubic perovskite-based
ferroelectric material KNbO3, it was demonstrated that the accuracy of the
method is sufficient for adequately describing the small energy differences
related to the ferroelectric instability. The choice of INDO parameters has
been done for a system containing Nb. Based on the parametrization proposed,
the electronic structure, equilibrium ground state structure of the
orthorhombic and rhombohedral phases, and Gamma-TO phonon frequencies in cubic
and rhombohedral phases of KNbO3 were calculated and found to be in good
agreement with the experimental data and with the first-principles calculations
available.Comment: 7 pages, 2 Postscript figures, uses psfig.tex. To be published in
Phys.Rev.B 54, No.4 (1996