<i>Ab initio</i>
            Hartree-Fock treatment of ionic and semi-ionic compounds: state of the art

Dovesi, Roberto; Roetti, C.; Freyria-Fava, C.; Aprà, Edoardo; Saunders, V. R.; Harrison, N. M.

doi:10.1098/rsta.1992.0094

Cited by 116 publications

(28 citation statements)

References 19 publications

(10 reference statements)

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“…Convergence of the solution at some geometries was unstable or slow but could be stabilized by the use of acceleration techniques such as ''level shifting.'' 34 In all states, the K atom is fully ionized to K ϩ and the charge is transferred to the substrate. The distinct types of electronic state obtained were as follows: First, with the donated electron delocalized over the surface to form a metallic system, secondly, with the electron localized on a particular surface or subsurface Ti site and, finally, states where charge was delocalized on more than one Ti ion.…”

Section: Resultsmentioning

confidence: 99%

“…34 Atom centered Gaussian functions with s, p, or d symmetry are used to describe the atomic orbitals. For comparison, electron exchange and correlation effects were treated using both HF and DFT-LDA ͑Refs.…”

Section: Computational Detailsmentioning

confidence: 99%

“…The k-space sampling was performed on a PackMonkhurst grid 34,43 of shrinking factor 4 yielding 18, 7, and 7 symmetry inequivalent points in the irreducible Brillouin zones of the bulk crystal and the (1ϫ1), and c(2ϫ2) ͑100͒ surface cells, respectively. This is sufficient to converge the surface structure to within 0.01 Å.…”

Section: Computational Detailsmentioning

confidence: 99%

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First-principles study of potassium adsorption onTiO2surfaces

1999

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We present an ab initio study of alkali metal adsorption on metal oxide surfaces. We have investigated the changes that occur to the structure and electronic properties of the rutile TiO 2 ͑100͒ surface when a 1 2 monolayer of potassium atoms is adsorbed. The K atoms are reduced to K ϩ ions as charge transfer occurs from the K 3s orbital to localized Ti 3d orbitals at the surface of the substrate. The occupied Ti 3d states lie about 1 eV above the O 2 p valence band maximum in agreement with recent photoemission studies. The Ti 3d states are spin polarized and are similar to those found at oxygen deficient TiO 2 surfaces. The geometric structure also undergoes significant relaxation as the lattice is polarized around the reduced Ti sites. The calculated surface structure is in excellent agreement with x-ray adsorption data. ͓S0163-1829͑99͒04224-1͔

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Section: Resultsmentioning

confidence: 99%

Section: Computational Detailsmentioning

confidence: 99%

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First-principles study of potassium adsorption onTiO2surfaces

1999

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“…We noticed that using 30 k points in the irreducible part of the BZ was sufficient to achieve aforesaid convergence both for HF and the LDA calculations performed with the CRYSTAL program. 33,44 Moreover, the excellent agreement observed among the HF energies/cell computed using the CRYSTAL program, our own WANNIER program, 29 and the finite-cluster-based HF calculations, leaves no doubt that the convergence in energies has been achieved.…”

Section: Applied Methods and Computational Detailsmentioning

confidence: 99%

“…For both systems HF calculations were performed first to obtain the results at the meanfield level. For the dimerized C chain, as well as for the BN chain, the HF calculations were performed in the infinite system limit using both the Bloch-orbital-based electronicstructure program CRYSTAL, 33,44 as well as our own Wannierfunction-based program WANNIER. 29 Both these programs use the linear combination of atomic-orbital approach based on Gaussian-type basis functions.…”

Section: Applied Methods and Computational Detailsmentioning

confidence: 99%

Ab initiomany-body calculations on infinite carbon and boron-nitrogen chains

2002

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In this paper we report first-principles calculations on the ground-state electronic structure of two infinite one-dimensional systems: ͑a͒ a chain of carbon atoms and ͑b͒ a chain of alternating boron and nitrogen atoms. Meanfield results were obtained using the restricted Hartree-Fock approach, while the many-body effects were taken into account by second-order Mo "ller-Plesset perturbation theory and the coupled-cluster approach. The calculations were performed using 6-31G** basis sets, including the d-type polarization functions. Both at the Hartree-Fock ͑HF͒ and the correlated levels, we find that the infinite carbon chain exhibits bond alternation with alternating single and triple bonds, while the boron-nitrogen chain exhibits equidistant bonds. In addition, we also performed density-functional-theory-based local-density-approximation ͑LDA͒ calculations on the infinite carbon chain using the same basis set. Our LDA results, in contradiction to our HF and correlated results, predict a very small bond alternation. Based upon our LDA results for the carbon chain, which are in agreement with an earlier LDA calculation ͓E.J. Bylaska, J.H. Weare, and R. Kawai, Phys. Rev. B 58, R7488 ͑1998͔͒, we conclude that the LDA significantly underestimates Peierls distortion. This emphasizes that the inclusion of many-particle effects is very important for the correct description of Peierls distortion in onedimensional systems.

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Unrestricted HF Calculations of Crystals with Strongly Correlated d‐Electron Subsystem: Chemical Bonding in Ti ₂ O ₃ Crystal

Ėvarestov

Leko

Veryazov

1998

phys. stat. sol. (b)

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Theoretical description of crystalline transition metal oxides is complicated by the coexistence of strongly localized atomic-like 3d-states and delocalized band states. As a result either insulating or metallic properties and the metal±insulator transition are observed in such crystals (for example, Ti 2 O 3 ).It is well known that the Hartree-Fock solutions corresponding to different electronic configurations may be found. In particular, it may be the result of different choice of the initial density matrix. In crystalline transition metal oxides d-electron states remain highly localized, and one can expect the dependence of the calculated electronic structure of a crystal on the electronic configuration of the constituent atoms. Moreover, one has to have in mind that the atomic states in a crystal are splitted up in accordance with the symmetry of the surrounding crystalline field.In the self-consistent HF-LCAO calculations the initial density matrix is taken by fixing the initial occupancies of basis atomic orbitals. Usually these occupancies are taken to be the same for different components of degenerated atomic orbitals. For example, when a minimal basis set is used, an atom with d 1 configuration (as in Ti 2 O 3 crystal), the initial occupancy for degenerated d-orbitals is usually taken to be 0.2e. However, for different choices of the initial density matrix the HF self-consistent procedure may lead to different solutions because the occupied and vacant states are considered in HF approximation with different potentials.In this work we have studied the electronic structure of Ti 2 O 3 crystal within unrestricted HF approximation using different initial occupancies for d-atomic orbitals of titanium atoms. Calculations of the electronic structure were performed by CRYSTAL95 code [1]. The pseudopotential atomic basis for Ti and O atoms was taken from [2]. The analysis of chemical bonding was made according to [3], extended to the case of periodic systems.Main electronic properties of Ti 2 O 3 crystal obtained in HF self-consistent calculations with different initial density matrices are listed in the table. Three groups of results correspond to density Rapid Research Notes R3

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Ab initio Hartree-Fock treatment of ionic and semi-ionic compounds: state of the art

Cited by 116 publications

References 19 publications

First-principles study of potassium adsorption onTiO2surfaces

First-principles study of potassium adsorption onTiO2surfaces

Ab initiomany-body calculations on infinite carbon and boron-nitrogen chains

Unrestricted HF Calculations of Crystals with Strongly Correlated d‐Electron Subsystem: Chemical Bonding in Ti ₂ O ₃ Crystal

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Ab initio Hartree-Fock treatment of ionic and semi-ionic compounds: state of the art

Cited by 116 publications

References 19 publications

First-principles study of potassium adsorption onTiO2surfaces

First-principles study of potassium adsorption onTiO2surfaces

Ab initiomany-body calculations on infinite carbon and boron-nitrogen chains

Unrestricted HF Calculations of Crystals with Strongly Correlated d‐Electron Subsystem: Chemical Bonding in Ti 2 O 3 Crystal

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Unrestricted HF Calculations of Crystals with Strongly Correlated d‐Electron Subsystem: Chemical Bonding in Ti ₂ O ₃ Crystal