Search results for "Ab initio quantum chemistry methods"
showing 10 items of 468 documents
Ab initio calculations of ABO3 perovskite (001), (011) and (111) nano-surfaces, interfaces and defects
2020
We carried out ab initio calculations for technologically important ABO3 perovskite, such as, SrTiO3, BaTiO3, SrZrO3 and PbZrO3 (001), (011) and (111) nano-surfaces, interfaces and bulk [Formula: see text]-centers. For SrTiO3, BaTiO3, SrZrO3 and PbZrO3 (001) nano-surfaces, as a rule, all first surface layer atoms relax inward, whereas all second layer atoms relax outward, and, typically, all third surface layer atoms, again, relax inward. Calculated (001) surface energies for SrTiO3, BaTiO3, SrZrO3 and PbZrO3 perovskites are almost equal for both BO2 and AO-terminations, and always smaller than the (011) and (111) surface energies. We discussed the results of our ab initio calculations dea…
Four-faceted nanowires generated from densely-packed TiO2 rutile surfaces: Ab initio calculations
2013
Abstract Two-dimensional (2D) slabs and monoperiodic (1D) nanowires orthogonal to the slab surface of rutile-based TiO 2 structure terminated by densely-packed surfaces and facets, respectively, have been simulated in the current study. The procedure of structural generation of nanowires (NWs) from titania slabs (2D → 1D) is described. We have simulated: ( i ) (110), (100), (101) and (001) slabs of different thicknesses as well as ( ii ) [001]- and [110]-oriented nanowires of different diameters terminated by either four types of related {110} facets or alternating { 1 1 ¯ 0 } and {001} facets, respectively. Nanowires have been described using both the Ti atom-centered rotation axes as well…
Ab initio modelling of silver adhesion on the corundum (0001) surface
2003
The Ag/a-Al2O3(0001) interface was simulated using ab initio slab calculations. We have studied silver adhesion on both Al- and Oterminated corundum substrates. The latter case may be considered as silver adhesion on a defective Al-terminated corundum surface with external aluminium vacancies. The dependence of the adhesion energy on the interfacial distance has been analyzed for the two favorable Ag adsorption positions and for two metal coverages (a 1/3 monolayer of the Ag(111) crystallographic plane and a full Ag(111) monolayer, 1 ML). The two different terminations (Al- and O-) give rise to qualitatively different results. In the former case, the small adhesion energies per Ag atom are …
Influence of the focusing effect on XAFS in ReO3, WO3−x and FeF3
1995
Abstract The role of the focusing effect in the formation of X-ray absorption fine structure (XAFS) is considered for ReO3, non-stoichiometric tungsten oxides WO3−x and FeF3 having the perovskite-type structure. Two cases are mainly discussed: (1) an admixture of rhenium and tungsten L2-edge XAFS in ReO3 and WO3−x crystals to the one above rhenium and tungsten L1-edge and (2) high-order superfocusing effect in Fe0F1Fe2F3Fe4 atomic chain in iron K-edge XAFS of FeF3 which is analysed using an ab initio multiple-scattering approach.
On the role of atomic thermal vibrations in binary-alloy thermodynamics
2001
An ab initio approach is advanced for the thermodynamical properties investigations of disordered binary alloys. Configurational and vibrational degrees of freedom are considered on the microscopic level in the grand partition sum calculations. Summing over the vibrational and configurational states of an alloy is performed within the reference system approach and the collective variables method, respectively. An equation defining the alloy free energy is obtained. The role of the atomic thermal vibrations in the binary-alloy thermodynamics and their relationship with the configurational effects are discussed. Conditions when the configurational and vibrational effects can be treated separa…
High-resolution Raman spectroscopy of the ν1 region and Raman-Raman double resonance spectroscopy of the 2ν1-ν 1 band of 32SF6 and 34SF 6. Determinat…
2004
The ν1 region of 32SF6 and 34SF6 has been studied by stimulated Raman spectroscopy. For both isotopomers, a detailed analysis has been performed. Several hot bands (ν1+ν6-ν6, ν1+2ν 6-2ν6, ν1+ν5-ν 5) have been taken into account to calculate synthetic spectra that satisfactorily reproduce the experimental data. These results, together with the previous studies of the other fundamental bands have allowed us to determine the equilibrium bond length of sulfur hexafluoride as r e=1.5560(1) Å, in very good agreement with recent ab initio calculations. The 2ν1-ν1 band has also been studied for both isotopomers by Raman-Raman double resonance spectroscopy and the resulting spectra have been analyze…
Ab initio hybrid DFT calculations of BaTiO3 bulk and BaO-terminated (001) surface F-centers
2017
Using a supercell model and a hybrid B3PW exchange-correlation functional, we have performed first principles calculations for the F-center in the BaTiO3 bulk and on the BaO-terminated (001) surface. We find that two Ti atoms nearest to the bulk F-center are repulsed, while nearest eight oxygen and four barium atoms relax toward the oxygen vacancy (by 1.06, 0.71 and 0.08% of the lattice constant [Formula: see text], respectively). The magnitudes of atomic displacements around the F-center located on the BaO-terminated (001) surface in most cases (except for Ti) are larger than those around the bulk F-center (0.1, 1.4 and 1.0% of [Formula: see text], respectively). Our calculated BaTiO3 bul…
Structural and electronic properties ofβ-FeSi2nanoparticles: The role of stacking fault domains
2014
We use conventional and aberration-corrected transmission electron microscopy (TEM) and ab initio calculations to investigate the structural and electronic properties of \ensuremath{\beta}-FeSi${}_{2}$ nanoparticles, which are a promising material for photovoltaic applications due to a band gap of 1 eV and a high absorption coefficient. The nanoparticles have average sizes of \ensuremath{\sim}20 nm, form aggregates, and are prepared by gas-phase synthesis. Amorphous SiO${}_{x}$ shells with thicknesses of \ensuremath{\sim}1.7 nm around \ensuremath{\beta}-FeSi${}_{2}$ cores are identified on individual nanoparticles using electron energy-loss spectroscopy, while stacking fault domains in the …
Ab initio calculations of MgF2 (001) and (011) surface structure
2010
We present the results of calculations of surface relaxations, rumplings, and charge distribution for the MgF2 (0 0 1) and (0 1 1) surfaces using ab initio code Crystal-2003 and the hybrid exchange-correlation B3PW functional. These two neutral and polar surfaces show very small relaxation and negligible increase of covalent contribution to the chemical bonding thus remaining considerably ionic. The calculated bulk optical band gap is in a good agreement with the experimental value, whereas optical band gap for the polar (0 1 1) surface is reduced by 0.6 eV compared with the calculated bulk value, in contrast to the (0 0 1) surface gap which remains very close to the bulk.
Ab initio hybrid DFT calculations of BaTiO3, PbTiO3, SrZrO3 and PbZrO3 (111) surfaces
2015
Abstract The results of ab initio calculations for polar BaTiO 3 , PbTiO 3 , SrZrO 3 and PbZrO 3 (111) surfaces using the CRYSTAL code are presented. By means of the hybrid B3LYP approach, the surface relaxation has been calculated for two possible B (B = Ti or Zr) or AO 3 (A = Ba, Pb or Sr) BaTiO 3 , PbTiO 3 , SrZrO 3 and PbZrO 3 (111) surface terminations. According to performed B3LYP calculations, all atoms of the first surface layer, for both terminations, relax inwards. The only exception is a small outward relaxation of the PbO 3 -terminated PbTiO 3 (111) surface upper layer Pb atom. B3LYP calculated surface energies for BaO 3 , PbO 3 , SrO 3 and PbO 3 -terminated BaTiO 3 , PbTiO 3 , …