R. D. King-Smith

A first-principles pseudopotential investigation of ferroelectricity in barium titanate

Abstract We have investigated the adiabatic energy surface of BaTiO3 using a first-principles molecular dynamics approach. High quality pseudopotentials were generated for barium, titanium and oxygen using a recently developed ultra-soft pseudopotential scheme. The wave-functions were expanded in a plane-wave basis set, and adequate convergence was achieved with a 25 Ry cutoff. We show that the method gives a good description of the ferroelectric properties of BaTiO3 and agrees well with recent first-principles calculations performed using the full-potential linear-augmented-plane-wave method.

Structural and electronic properties of sodium metasilicate

Abstract The structure of sodium metasilicate has been determined for the first time based on a first-principles calculation. The total energy expressed in the local-density approximation is minimized using a preconditioned conjugate gradient algorithm. The Vanderbilt ultrasoft pseudopotenial scheme is adopted to improve the computational efficiency. All the structural parameters obtained agree very well with experimental results. Also, the band structure and electron density of states are calculated and compared with experiments and other theoretical studies.

Coulomb interaction and ferroelectric phase transitions in perovskite compounds

We approach the problem of ferroelectricity in cubic perovskite compounds by a three-stage procedure. First, a systematic set of first-principles calculations of structural energies and Coulomb interactions is carried out. We review this work, with an emphasis on the calculation of the Born effective charges, which we find to have anomalously large values. Second, these results are used to construct a model Hamiltonian for BaTiO3 with parameters fixed from the ab initio calculations. Third, we employ this Hamiltonian in a Monte-Carlo simulation of the ferroelectric phase transitions of BaTiO3. We obtain the correct experimental transition sequence cubic → tetragonal → orthorhombic → rhombohedral with decreasing temperature, but we underestimate the transition temperatures. This discrepancy is attributed to a small error in the ab initio lattice constant.

Pseudopotential total-energy calculations of column-V acceptors in ZnSe

Abstract We demonstrate the applicability of a recently developed ultra-soft pseudopotential scheme to the study of point defects in II-VI semiconductors. While conventional pseudopotentials typically treat all but the most loosely bound atomic levels as core states, the present scheme allows us to treat the Zn 3d states with a modest plane-wave cutoff, and thus to include the Zn d-shell as a valence shell. Moreover, the nitrogen p-states can be treated as easily as those of the heavier column-V dopants within this scheme. As a preliminary application, we study the total energy of column-V acceptors (N, P and As) as a function of structural degrees of freedom in ZnSe, with particular attention to the bond-breaking instability which has been proposed by Chadi as a mechanism for dopant self-compensation.