Defect Studies in Silicon Dioxide by Local Density Approximation Total Energy Methods

1988 ◽  
Vol 141 ◽  
Author(s):  
Douglas C. Allan ◽  
Michael P. Teter ◽  
John D. Joannopoulos ◽  
Yaneer Bar-Yam ◽  
Sokrates T. Pantelides
Keyword(s):  
Oxygen Vacancy ◽  
Silicon Dioxide ◽  
Total Energy ◽  
Local Density Approximation ◽  
Local Density ◽  
Energy Methods ◽  
Density Approximation ◽  
Charge Densities ◽  
Preliminary Results ◽  
Total Energies

AbstractThe oxygen vacancy in silicon dioxide is currently believed to explain one of the most important defects observed in this material, the E1 ' center. To get a better understanding of the oxygen vacancy, we have investigated the equilibrium geometric structures, total energies, and charge densities of several charge states of the defect in alpha cristobalite. We also present some preliminary results for alpha quartz.

Effects of ternary additions on the twin energy and site preference in γ-TiAl

1994 ◽  
Vol 9 (7) ◽  
pp. 1755-1760 ◽  
Author(s):  
Jian-hua Xu ◽  
A.J. Freeman
Keyword(s):  
Total Energy ◽  
Local Density Approximation ◽  
Relative Stability ◽  
Local Density ◽  
Site Preference ◽  
Density Approximation ◽  
Self Consistent ◽  
Ternary Additions

Site preference and the effects of ternary additions (Mn, V, etc.) on the twin energy in γ-TiAl were studied by means of all-electron total energy self-consistent calculations based on the local density approximation. The results show that when Mn, Ti, or V substitute on the Al-sites in γ-TiAl, the twin energy is about 20–25% lower than that of stoichiometric γ-TiAl; this may explain observations of increased twinning activity in 48% Al TiAl. By contrast, when ternary additions of V (or Al) occupy Ti-sites, the twin energy has nearly the same value as that of pure γ-TiAl, which is consistent with the observation of only a few twins for Al-rich compositions. By comparing the total energy of Ti6(XAl5) and (Ti5X)Al6 supercells, it is found that the relative stability of Ti6(XAl5) over (Ti5X)Al6 (i.e., the preference for occupying Al-sites) is increased in going from Nb, V, Cr, and Ti to Mn, in agreement with observation that excess Ti occupies Al-sites, and Nb preferentially substitutes on the Ti-sites. The results indicate that Mn preferentially substitutes on the Al-sites, and V (or Cr) may occupy both Ti- and Al-sites.

Pseudoatomic Orbital Compact Basis Sets: Applications to Metallic Systems

1988 ◽  
Vol 141 ◽  
Author(s):  
Robert W. Jansen ◽  
B. H. Klein
Keyword(s):  
Free Electron ◽  
Local Density Approximation ◽  
Local Density ◽  
Low Energy ◽  
Basis Sets ◽  
Density Approximation ◽  
Self Consistent ◽  
Total Energies ◽  
Energy Convergence ◽  
Metallic Systems

AbstractA self-consistent orbital-based scheme is applied to metallic systems and is found to be efficient for these materials. The technique uses the local density approximation in the pseudopotential framework, but replaces the planewave basis by a basis pseudoatomic orbitals constructed directly from the pseudoatoms. Free electron-like wavefunction components are handled by orthogonalizing the orbital basis to a few low energy planewaves as needed for good eigenvalue and total energy convergence. The method is fast and versatile enough to be used for a variety of problems. Applications to bulk bandstructures, total energies, and forces in Al and Nb are presented.

Ab initio total energy studies of minerals using density functional theory and the local density approximation

1995 ◽  
Vol 59 (397) ◽  
pp. 589-596 ◽  
Author(s):  
Björn Winkler ◽  
Victor Milman ◽  
Michael C. Payne
Keyword(s):  
Total Energy ◽  
Ab Initio ◽  
Local Density Approximation ◽  
Density Functional ◽  
Local Density ◽  
Lattice Energy ◽  
Density Approximation ◽  
Proton Proton ◽  
Energy Calculations ◽  
Good Agreement

AbstractAb initio total energy calculations based on the local density approximation (LDA) and using a conjugate-gradient solver for the Kohn-Sham equations have been performed for cordierite, brucite, (Mg(OH)2) and diaspore (AlOOH). The calculated fractional coordinates of all structures are in good agreement with experimental diffraction data. The angle of the non-linear hydrogen bond in diaspore is reproduced well. The Raman active OH stretching frequency in brucite has been calculated using the frozen phonon approach and the calculated stretching frequency is in very good agreement with the observed value. The energetically most favourable calculated orientation of the proton-proton vector of an H2O molecule incorporated in the structural channels of cordierite agrees with findings deduced from spectroscopic data, and the calculated energy of hydration is in reasonable agreement with calorimetric data. It is therefore concluded that ab initio total energy calculations can confidently be used to predict properties of hydrogen bonded structures, which is difficult with conventional parameterized static lattice energy minimization calculations. An extension to the model is necessary to improve the agreement of the predicted to the observed lattice parameters for small structures.

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