Showing papers by "John W. Mintmire published in 1999"

Energetics of aluminum vacancies in gamma alumina

Abstract: We present results for total-energy simulations of the energetics of vacancy occupation of \ensuremath{\gamma} alumina using an empirical potential that allows the ionic valence to vary according to the local environment and includes Coulombic electrostatic interactions among the anions and cations. Our model predicts that although the minimum enthalpy configuration has all aluminum vacancies from the spinel structure in octahedral sites, the energetic cost of a modest fraction of tetrahedral sites is small. We furthermore use our model to explain the differences between previously reported simulations on this question in terms of their constraints on structural and charge relaxation.

Calculation of the Total Energy Per Unit Cell and of the Band Structures of the Five Nucleotide Base Stacks Using the Local-density Approximation

Abstract: All-electron first-principles total energy electronic structure calculations were carried out for single chains of four nucleotide base stacks (composed of adenine, thymine, guanine, and cytosine, respectively) in the DNA B conformation (3.36 A stacking distance and 36° screw angle θ) using the local-density approximation (LDA) within a helical band structure approach. A uracil stack was also computed in the DNA B conformation and compared with the results obtained for the four DNA base stacks. The total energies per unit cell as a function of the stacking distance (at fixed screw angle θ=36°) and of the screw angle (at d=3.36 A) show in most cases rather good agreement with the experiment. As expected with LDA calculations, the band gaps were underestimated by nearly 50% compared to experimentally suggested values. Finally, some suggestions are given for the improvement of the band structures of the nucleotide base stacks.