Recent Advances in Non Self-Consistent Total Energy Calculations in Alloys

1990 ◽  
Vol 186 ◽  
Author(s):  
M. van Schilfgaarde ◽  
A.T. Paxton ◽  
A. Pasturel ◽  
M. Methfessel
Keyword(s):  
Phase Diagram ◽  
Total Energy ◽  
First Principles ◽  
Materials Science ◽  
Local Density ◽  
Tight Binding ◽  
Density Approximation ◽  
Energy Calculations ◽  
Self Consistent ◽  
Mixing Enthalpies

In recent years, total energy calculations based on the local density approximation (LDA) have begun to find applications in materials science [1]. In the context of the present symposium, the most relevant application is to the calculation of total and relative energies of ordered alloy phases and their mixing enthalpies. The first-principles LDA approach is now taking over from tight-binding or simple empirical schemes in providing input to phase diagram calculations, for example, using Connolly-Williams inversion [2]. We wish to make two points in our contribution to the symposium.

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.

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.

scholarly journals Density-functional Based Tight-binding Calculations on Thiophene Polymorphism

VLSI Design ◽  
2001 ◽  
Vol 13 (1-4) ◽  
pp. 393-397
Author(s):  
J. Widany ◽  
G. Daminelli ◽  
A. Di Carlo ◽  
P. Lugli
Keyword(s):  
Total Energy ◽  
Intermolecular Interaction ◽  
Density Functional ◽  
Tight Binding ◽  
Methyl Groups ◽  
Direct Function ◽  
Energy Calculations ◽  
Polymorphic Modifications

Total energy calculations based on a density-functional tight-binding scheme have been performed on polymorphic modifications of various thiophene crystals. The investigated structures include sulphanyl-substituted quater-thiophene and methyl-substituted sexithiophene, in the monoclinic and triclinic modifications. Attention has been focused on the intermolecular interaction between the molecular units. Despite the similarities in the backbone geometries, the strength and nature of intermolecular interaction differs largely in the various polymorphs. Sulphur atoms belonging to the thiophene rings are strongly involved in the interaction. Sulphanyl substituents play an important role, while methyl groups do not contribute. The strength of intermolecular interaction is not a direct function of atom distance.

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