Showing papers by "Francesco Mauri published in 1996"

Ab Initio Theory of NMR Chemical Shifts in Solids and Liquids.

Abstract: We present a theory for the {ital ab} {ital initio} computation of NMR chemical shifts ({sigma}) in condensed matter systems, using periodic boundary conditions. Our approach can be applied to periodic systems such as crystals, surfaces, or polymers and, with a supercell technique, to nonperiodic systems such as amorphous materials, liquids, or solids with defects. We have computed the hydrogen {sigma} for a set of free molecules, for an ionic crystal LiH, and for a H-bonded crystal HF, using density functional theory in the local density approximation. The results are in excellent agreement with experimental data. {copyright} {ital 1996 The American Physical Society.}

Density-functional theory of the nonlinear optical susceptibility: Application to cubic semiconductors.

Abstract: We present a general scheme for the computation of the time-dependent (TD) quadratic susceptibility (${\mathrm{\ensuremath{\chi}}}^{(2)}$) of an extended insulator obtained by applying the ``2n+1'' theorem to the action functional as defined in TD density-functional theory. The resulting expression for ${\mathrm{\ensuremath{\chi}}}^{(2)}$ includes self-consistent local-field effects, and is a simple function of the linear response of the system. We compute the static ${\mathrm{\ensuremath{\chi}}}^{(2)}$ of nine III-V and five II-VI semiconductors using the local density approximation (LDA), obtaining good agreement with experiment. For GaP we also evaluate the TD ${\mathrm{\ensuremath{\chi}}}^{(2)}$ for second-harmonic generation using TD-LDA. \textcopyright{} 1996 The American Physical Society.

Magnetic susceptibility of insulators from first principles

Abstract: We present an {ital ab} {ital initio} approach for the computation of the magnetic susceptibility {chi} of insulators. The approach is applied to compute {chi} in diamond and in solid neon using density functional theory in the local density approximation, obtaining good agreement with experimental data. In solid neon, we predict an observable dependence of {chi} upon pressure. {copyright} {ital 1996 The American Physical Society.}

Phonon Softening and Superconductivity in Tellurium under Pressure.

Abstract: The phonon dispersion and the electron-phonon interaction for the {beta}-Po and the bcc high pressure phases of tellurium are computed with density-functional perturbation theory. Our calculations reproduce and explain the experimentally observed pressure dependence of the superconducting critical temperature ({ital T}{sub {ital c}}) and confirm the connection between the jump in {ital T}{sub {ital c}} and the structural phase transition. The phonon contribution to the free energy is shown to be responsible for the difference in the structural transition pressure observed in low and room temperature experiments. {copyright} {ital 1996 The American Physical Society.}