Calculations of Atomic and Electronic Structure for (100) Surfaces of SrTiO3 Perovskite

2002 ◽  
Vol 718 ◽  
Author(s):  
R. I. Eglitis ◽  
E. Heifets ◽  
E. A. Kotomin ◽  
G. Borstel
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Computer Code ◽  
Basis Set ◽  
Surface Relaxation ◽  
Functional Theory ◽  
Exchange Correlation ◽  
Hartree Fock ◽  
Atomic And Electronic Structure

AbstractWe present and discuss main results of the calculations for the surface relaxation and rumpling of SrTiO3 surfaces with TiO2 and SrO terminations using a wide variety of methods of modern computational physics and chemistry, including the shell model (SM) and ab initio methods based on Hartree-Fock (HF) and Density Functional Theory (DFT). The HF and DFT formalisms with different exchange-correlation functionals are implemented into Crystal-98 computer code using a Gaussian-type basis set. We demonstrate that a hybrid B3PW formalism gives the best results for the bulk SrTiO3 properties. Results are compared with previous ab initio plane-wave LDA calculations and LEED experiments. Our calculations demonstrate an increase of the covalency effects between Ti and O atoms near the surface.

Conformational and Vibrational Analysis of 2,4-, 2,5- and 2,6-Difluorobenzaldehydes by ab initio Hartree-Fock and Density Functional Theory Calculations

2008 ◽  
Vol 63 (3-4) ◽  
pp. 175-182 ◽  
Author(s):  
Adnan Sağlam ◽  
Fatih Ucun
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Vibrational Analysis ◽  
Molecular Structures ◽  
Basis Set ◽  
Functional Theory ◽  
Vibrational Assignments ◽  
Hartree Fock ◽  
The Mean

The optimized molecular structures, vibrational frequencies and corresponding vibrational assignments of the two planar O-cis and O-trans rotomers of 2,4-, 2,5- and 2,6-difluorobenzaldehyde have been calculated using ab initio Hartree-Fock (HF) and density functional theory (B3LYP) methods with the 6-311++G(d,p) basis set level. The calculations were adapted to the CS symmetries of all the molecules. The O-trans rotomers with lower energy of all the compounds have been found as preferential rotomers in the ground state. The mean vibrational deviations between the vibrational frequency values of the two conformers of all the compounds have been shown to increase while the relative energies increase, and so it has been concluded that the higher the relative energy between the two conformers the bigger is the mean vibrational deviation.

Ab Initio Hartree-Fock and Density Functional Theory Study on Molecular Structures, Energies, and Vibrational Frequencies of 2-Amino-3-, 4-, and 5-Nitropyridine

2010 ◽  
Vol 65 (1-2) ◽  
pp. 107-112 ◽  
Author(s):  
Yusuf Sert ◽  
Fatih Ucun ◽  
Mustafa Böyükata
Keyword(s):  
Experimental Data ◽  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Vibrational Frequencies ◽  
Geometric Parameters ◽  
Molecular Structures ◽  
Basis Set ◽  
Functional Theory ◽  
Hartree Fock

AbstractThe molecular structures, vibrational frequencies, and corresponding vibrational assignments of 2-amino-3-, 4-, and 5-nitropyridine have been calculated by using ab initio Hartree-Fock (HF) and density functional theory (B3LYP) methods with 6-311++G(d,p) basis set level. The calculated vibrational frequencies and optimized geometric parameters (bond lengths and bond angles) were found to be in well agreement with the experimental data. The comparison of the observed and the calculated results showed that the scaled B3LYP method is superior to the scaled HF method for both the vibrational frequencies and the geometric parameters. For well fitting the calculated and the experimental frequencies we used scale factors obtained from the ratio of the frequency values of the strongest peaks in the calculated and the experimental spectra. These obtained scales seem to cause the better agreement of the gained vibrations to the experimental data.

scholarly journals Density Functional Theory and Complete Basis Set Ab Initio Computational Study of Five-, Six-, Seven- and Eight-hydrogen Coordinated Carbon Cations

1999 ◽  
Vol 23 (8) ◽  
pp. 502-503
Author(s):  
Branko S. Jursic
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Computational Study ◽  
Basis Set ◽  
Functional Theory ◽  
Complete Basis ◽  
Complete Basis Set ◽  
High Level

High level ab initio and density functional theory studies are performed on highly protonated methane species.

scholarly journals Density functional tight binding: values of semi-empirical methods in an ab initio era

2014 ◽  
Vol 16 (28) ◽  
pp. 14368-14377 ◽  
Author(s):  
Qiang Cui ◽  
Marcus Elstner
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Tight Binding ◽  
Empirical Methods ◽  
Functional Theory ◽  
Hartree Fock ◽  
Semi Empirical

Semi-empirical (SE) methods are derived from Hartree–Fock (HF) or Density Functional Theory (DFT) by neglect and approximation of electronic integrals.

Ab initio Correlation Effects in Density Functional Theories: An Electron-Distribution-Based Study for Neon

2005 ◽  
Vol 70 (8) ◽  
pp. 1157-1176 ◽  
Author(s):  
Karol Jankowski ◽  
Ireneusz Grabowski ◽  
Krzysztof Nowakowski ◽  
Jan Wasilewski
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Physical Nature ◽  
Correlation Effects ◽  
Functional Theory ◽  
Exchange Correlation ◽  
Hartree Fock ◽  
Brueckner Orbitals ◽  
Local Gradient ◽  
The Impact

We have briefly reviewed the idea of studies aiming at such a bridging of the methodological gap between ab initio methods (or wave function theory (WFT)) and density functional theory (DFT) that would afford carrying over results concerning details of the structure of correlation effects from one method to the other. Special attention is paid to the problem of coverage of the WFT correlation effects by the exchange-correlation functionals of DFT. A short survey of the concept of supplementing energy-based investigations in this field by electron-density-based studies is given and illustrated by results for the Ne atom. DFT densities are generated for representatives of all four generations of presently used exchange-correlation functionals, including the recently developed orbital-dependent one. These densities are compared with WFT densities calculated at the MP2, MP3, and Brueckner determinant levels. It is found that the exchange-only parts of the local, gradient-corrected, and hybrid functionals account for the bulk of WFT correlation effects. The impact of the associated correlation functionals is very small and their physical nature is not quite clear. The situation is different for the orbital-dependent functional for which the exchange-only functional provides an almost exact description of the Hartree-Fock density. Here, the correlation effects are entirely represented by the correlation functional. Attention is also paid to the suitability of Kohn-Sham orbitals for the description of WFT correlation effects and to their presumptive similarity with Brueckner orbitals.

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