Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

We present ab initio quantum-mechanical molecular-dynamics simulations of the liquid-metal--amorphous-semiconductor transition in Ge. Our simulations are based on (a) finite-temperature density-functional theory of the one-electron states, (b) exact energy minimization and hence calculation of the exact Hellmann-Feynman forces after each molecular-dynamics step using preconditioned conjugate-gradient techniques, (c) accurate nonlocal pseudopotentials, and (d) Nos\'e dynamics for generating a canonical ensemble. This method gives perfect control of the adiabaticity of the electron-ion ensemble and allows us to perform simulations over more than 30 ps. The computer-generated ensemble describes the structural, dynamic, and electronic properties of liquid and amorphous Ge in very good agreement with experiment. The simulation allows us to study in detail the changes in the structure-property relationship through the metal-semiconductor transition. We report a detailed analysis of the local structural properties and their changes induced by an annealing process. The geometrical, bonding, and spectral properties of defects in the disordered tetrahedral network are investigated and compared with experiment.

Ab initio molecular-dynamics simulation of the liquid-metal-amorphous-semiconductor transition in germanium.

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

To use solar irradiation or interior lighting efficiently, we sought a photocatalyst with high reactivity under visible light. Films and powders of TiO 2- x N x have revealed an improvement over titanium dioxide (TiO 2 ) under visible light (wavelength 2 has proven to be indispensable for band-gap narrowing and photocatalytic activity, as assessed by first-principles calculations and x-ray photoemission spectroscopy.

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Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxides

The linearized-augmented-plane-wave (LAPW) method for thin films is generalized by removing the remaining shape approximation to the potential inside the atomic spheres. A new technique for solving Poisson's equation for a general charge density and potential is described and implemented in the film LAPW method. In the resulting full-potential LAPW method (FLAPW), all contributions to the potential are completely taken into account in the Hamiltonian matrix elements. The accuracy of the method---already well known for clean metal surfaces---is demonstrated for the case of a nearly free (noninteracting) ${\mathrm{O}}_{2}$ molecule which is a severe test case of the method because of its large anisotropic charge distribution. Detailed comparisons show that the accuracy of the FLAPW results for ${\mathrm{O}}_{2}$ exceeds that of existing state-of-the-art local-density linear-combination-of-atomic-orbitals (LCAO)-type calculations, and that taking the full potential LAPW results as a reference, the LCAO basis can be improved by adding off-site functions. Thus the full-potential LAPW is a unified method which is ideally suited to test not only molecular adsorption on surfaces, but also the components of the same system separately, i.e., the extreme limits of the molecule and the clean surface.

Full-potential self-consistent linearized-augmented-plane-wave method for calculating the electronic structure of molecules and surfaces: O 2 molecule

Total-energy all-electron density functional method for bulk solids and surfaces

Results of all-electron self-consistent semirelativistic full-potential linearized augmented-plane-wave local-density and local-spin-density studies are reported for a seven-layer Fe(001) thin film. The calculated work function for the ferromagnetic state is found to be in excellent agreement with experiment, whereas that calculated for the paramagnetic state is significantly worse (namely, 0.5 eV too large), indicating the importance of spin polarization on this electrostatic property. For both states, partial densities of states (projected by layer and by orbital angular momentum), surface states, and charge (and spin) densities are presented and their differences employed to discuss the origin of surface magnetism. No Friedel oscillation is found in the layer-by-layer charge density. The surface-layer magnetic moment is found to have been increased by 0.73${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ from the center layer to 2.98${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$/atom; a very small Friedel oscillation is obtained for the spin density, which indicates possible size effects in this seven-layer film. Layer-by-layer Fermi contact hyperfine fields are presented: While the core-polarization contributions are proportional to the magnetic moment, the conduction-electron contribution shows a pronounced Friedel oscillation in the central layer and, significantly, a change of sign and increase in the magnitude for the surface-layer contribution. The hyperfine field at the nucleus of the center-layer atoms is found to be in excellent agreement with experiment. The net result for the surface-layer atoms is a predicted decrease in magnitude of the total Fermi contact hyperfine field despite the large increase of their magnetic moments. The relevance of this prediction to experiment is discussed.

Surface magnetism of Fe(001)

Prediction of electronic interlayer states in graphite and reinterpretation of alkali bands in graphite intercalation compounds

The explicit inclusion of fractional occupation numbers in density-functional calculations is shown to require an additional term to make the energy functional variational. The contribution from this term to the density-functional force exactly cancels the correction term depending on changes in the occupation number. For occupation numbers obeying a Fermi distribution, the resulting functional is identical in form to the grand potential; other choices for the form of the occupation numbers will result in different functionals. These terms, although numerically small, should be included in practical calculations that allow for fractional occupation numbers.

Michael Weinert

Papers

Full-potential self-consistent linearized-augmented-plane-wave method for calculating the electronic structure of molecules and surfaces: O 2 molecule

Total-energy all-electron density functional method for bulk solids and surfaces

Surface magnetism of Fe(001)

Prediction of electronic interlayer states in graphite and reinterpretation of alkali bands in graphite intercalation compounds

Fractional occupations and density-functional energies and forces.