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Ab initio calculations of the superconducting properties have been performed for zirconium and hafnium nitrides at normal and high pressures. The results for ZrN are in good agreement with the existing data of the tunnel experiments and measurements of the pressure derivative of the critical temperature T c. It has been shown that the decrease in T c under compression occurs due primarily to an increase in the phonon frequencies. [ABSTRACT FROM AUTHOR]

We report ab initio linear-response calculations 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 agree well with the experiment. Factors accounting for the relatively low critical temperatures T c in transition metal compounds with light elements are considered and the possible ways of increasing T c are discussed. [ABSTRACT FROM AUTHOR]

A brief review is given on the studies of ferroelectricity in perovskites. Early phenomenological theories of displacement-type ferroelectrics are considered. Two markedly different approaches based on density-functional theory are described. In one approach, the electron density of crystal is determined as a sum of Bloch functions. In the other, it is constructed as a superposition of the electron densities of individual ions. The latter approach gives a microscopic justification for the old phenomenological theories. We show that some phenomena in perovskites, which seemingly are of the order-disorder origin, can be explained by quasi-one-dimensional peculiarities of lattice dynamics. [ABSTRACT FROM AUTHOR]

Abinitio calculations of the superconducting properties have been performed for niobium carbide (NbC) at normal pressure and upon a 15 and 30% compression. Factors accounting for the relatively low values of the transition temperature Tc in transition metal carbides are considered and the possible ways of increasing this parameter are discussed. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]