Showing papers by "Francesco Mauri published in 1997"

Structure, Bonding, and Geochemistry of Xenon at High Pressures

Abstract: Although xenon becomes metallic at pressures above about 100 gigapascals, a combination of quantum mechanical calculations and high pressure–temperature experiments reveals no tendency on the part of xenon to form a metal alloy with iron or platinum to at least 100 to 150 gigapascals. The transformation of xenon from face-centered cubic (fcc) to hexagonal close-packed (hcp) structures is kinetically hindered, the differences in volume and bulk modulus between the two phases being smaller than we can resolve (less than 0.3 percent and 0.6 gigapascals, respectively). The equilibrium fcc-hcp phase boundary is at 21 (±3) gigapascals, which is a lower pressure than was previously thought, and it is unlikely that Earth9s core serves as a reservoir for primordial xenon.

Ab initio NMR Chemical Shift of Diamond, Chemical-Vapor-Deposited Diamond, and Amorphous Carbon

Abstract: The NMR chemical shift spectra of diamond, chemical-vapor-deposited (CVD) diamond, and diamondlike amorphous carbon are computed from first principles. The results of our calculation are in excellent agreement with experiments, and are useful for the interpretation of the NMR spectra in terms of the microscopic structure of the materials. In particular, we show that the NMR and Raman linewidths in polycrystalline CVD diamond are due to stress fluctuations, and we support a heterogeneous model for the amorphous hydrogenated phase. {copyright} {ital 1997} {ital The American Physical Society}

Magnetic susceptibility of semiconductors by an all-electron first-principles approach

Abstract: The magnetic susceptibility $(\ensuremath{\chi})$ of the semiconductors (diamond, Si, GaAs, and GaP) and of the inert-gas solids (Ne, Ar, and Kr) are evaluated within density-functional theory in the local-density approximation, using a mixed-basis all-electron approach. In Si, GaAs, GaP, Ar, and Kr, the contribution of core electrons to $\ensuremath{\chi}$ is comparable to that of valence electrons. However, our results show that the contribution associated with the core states is independent of the chemical environment and can be computed from the isolated atoms. Moreover, our results indicate that the use of a ``scissor operator'' does not improve the agreement of the theoretical $\ensuremath{\chi}$ with experiments.

First-principles wannier functions of silicon and gallium arsenide

Abstract: We present a self-consistent, real-space calculation of the Wannier functions of Si and GaAs within density-functional theory. We minimize the total-energy functional with respect to orbitals which behave as Wannier functions under crystal translations and, at the minimum, are orthogonal. The Wannier functions are used to calculate the total energy, lattice constant, bulk modulus, and the frequency of the zone-center TO phonon of the two semiconductors with the accuracy required in ab initio calculations. Furthermore, the centers of the Wannier functions are used to compute the macroscopic polarization of Si and GaAs in zero electric field. The effective charges of GaAs, obtained by finite differentiation of the polarization, agree with the results of linear-response theory.

First-Principles Wannier Functions for silicon and gallium arsenide

Abstract: We present a self-consistent, real-space calculation of the Wannier functions of Si and GaAs within density functional theory. We minimize the total energy functional with respect to orbitals which behave as Wannier functions under crystal translations and, at the minimum, are orthogonal. The Wannier functions are used to calculate the total energy, lattice constant, bulk modulus, and the frequency of the zone-center TO phonon of the two semiconductors with the accuracy required nowadays in ab-initio calculations. Furthermore, the centers of the Wannier functions are used to compute the macroscopic polarization of Si and GaAs in zero electric field. The effective charges of GaAs, obtained by finite differentiation of the polarization, agree with the results of linear response theory.