Asphericity effects in the electron density of VF<sub>2</sub>

Costa, Μ. M. R.; Almeida, M. J. M. de

doi:10.1107/s010876818709774x

Cited by 5 publications

(2 citation statements)

References 5 publications

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“…KF is a simple binary fluoride with the AB rock-salt structure. 59 VF 2 60 and MnF 2 61 exhibit the AB 2 rutile structure. KMnF 3 62 exhibits the ABX 3 perovskite structure whereas Na 3 ScF 6 63 and Na 3 MnF 6 64 are ordered double perovskites with the cryolite structure-Na occupies both the A and B positions in the A 2 B 2 X 6 structure.…”

Section: Compounds and Crystal Datamentioning

confidence: 99%

Assessing exchange-correlation functional performance for structure and property predictions of oxyfluoride compounds from first principles

Charles

Rondinelli

2016

Phys. Rev. B

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Motivated by the resurgence of electronic and optical property design in ordered fluoride and oxyfluoride compounds, we present a density functional theory (DFT) study on 19 materials with structures, ranging from simple to complex, and variable oxygen-to-fluorine ratios. We focus on understanding the accuracy of the exchange-correlation potentials (Vxc) to DFT for the prediction of structural, electronic, and lattice dynamical properties at four different levels of theory, i.e., the local density approximation (LDA), generalized gradient approximation (GGA), metaGGA, and hybrid functional level which includes fractions of exact exchange. We investigate in detail the metaGGA functionals MS2 [Sun et al., Phys. Rev. Lett., 111, 106401 (2013)] and SCAN [Sun et al., Phys. Rev. Lett., 115, 036402 (2015)], and show that although the metaGGAs show improvements over the LDA and GGA functionals in describing the electronic structure and phonon frequencies, the static structural properties of fluorides and oxyfluorides are often more accurately predicted by the GGA-level functional PBEsol. Results from LDA calculations are unsatisfactory for any compound regardless of oxygen concentration. PBEsol or HSE06 gives good performance in all oxide or all fluoride compounds. For the oxyfluorides, PBEsol is consistently more accurate for structural properties across all oxygen concentrations, however, we stress the need for detailed property assessment with various functionals for oxyfluorides with variable composition. The "best" functional is anticipated to be more strongly dependent on the property of interest. Our study provides useful insights in selecting an Vxc that achieves the best performance comprise, enabling more accurate predictive design of functional fluoride-based materials with density functional theory.

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Section: Compounds and Crystal Datamentioning

confidence: 99%

Assessing exchange-correlation functional performance for structure and property predictions of oxyfluoride compounds from first principles

Charles

Rondinelli

2016

Phys. Rev. B

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“…A derivation of ¿/-orbital occupancies from multipolar expansion coefficients c tm is given by Stevens and Coppens (1979) and applied to pyrite by Stevens, de Lucia and Coppens (1979). A similar attempt was made by Costa and de Almeida (1987) to determine ¿/-orbital occupancies of vanadium in VF 2 but with the simplification that the orthorhombic symmetry mmm was treated as if it were tetragonal 4/mmm.…”

Section: Orbitalsmentioning

confidence: 99%

Multipole- and orbital-occupancies deduced from X-ray diffraction intensities by means of combined least-squaresand crystal field perturbation-calculations

Gonschorek¹

1989

Zeitschrift Für Kristallographie - Crystalline Materials

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Multipole occupation parameters least-squares refined on the basis of X-ray diffraction intensities are combined with orbital occupation parameters obtained from crystal field perturbation-calculations using the model of point charges situated on the atomic positions. As the result preliminary orbital occupation parameters are obtained and these themselves are least-squares refined on the basis of the observed intensities. The point charges are superposed by the charge distributions of the occupied orbitals and the perturbation calculation is again carried out. The crystal field is calculated by summation in reciprocal space. The self potential is taken into account. The perturbation calculation yields besides of orbital occupation parameters also crystal field energy levels. MultipolesThe charge distribution ρ ν (Γ) of a v-th "pseudoatom" in the crystal field may be partitioned into the charge distribution ρ{(τ) of the free atom or ion and its deformation density ζ1ρ ν (Γ): ρ ν (Γ) = ρ{(Γ) + Λρ ν (Γ).(1)The deformation density can be expanded in spherical harmonics + 1 ¿0v(r) = Σ Σ RÌJr)N lm c] m P lm (cosö)^* (2)I m = -I Brought to you by | University of California Authenticated Download Date | 6/7/15 8:37 PM

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Electronic properties of the two rutiles TiO₂ and VF₂: A comparative study

Springborg

Asthalter

Weyrich

1998

Ber Bunsenges Phys Chem

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Results of first‐principles, density‐functional LMTO‐ASA calculations on the two title compounds and of unrestricted Hartree‐Fock (UHF) calculations on VF2 are reported. The calculations on the crystalline materials were performed with special emphasis on optimising all (three) structural parameters, on the valence density of states and the valence electron density, and on the possible existence of spin polarisation. In addition, full‐potential LMTO calculations on isolated monomers were carried through in order to examine the nearest‐neighbour (TiO and VF) chemical bonds in detail and to understand the consequences of various approximations in describing the potential for the crystal. The LMTO‐ASA calculations reproduce the correct lattice constants with, however, some overestimate for VF2. Also the nearest‐neighbour TiO and VF bond lengths are reproduced correctly by the LMTO calculations, whereas the c/a ratios are significantly overestimated. By analysing the charge densities of the isolated monomers we conclude that the overestimates in the c/a ratios are due to the ASA (Atomic‐Sphere Approximation), which does not describe the quadrupole‐quadrupole interactions of the compounds sufficiently accurately. The Hartree‐Fock calculations yield lattice constants for VF2 very close to experiment. Also in agreement with experiment, TiO2 is found to be non‐magnetic and insulating/semiconducting. In contrast, VF2 is found to be metallic within the LMTO‐ASA method, although the density‐functional calculations indicate that magnetic effects will change the compound into an insulator as it is according to experiment. On the other hand, in agreement with experimental evidence, UHF yields a non‐metallic structure. It further shows the stability of a number of patterns of magnetic ordering.

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Asphericity effects in the electron density of VF₂

Cited by 5 publications

References 5 publications

Assessing exchange-correlation functional performance for structure and property predictions of oxyfluoride compounds from first principles

Assessing exchange-correlation functional performance for structure and property predictions of oxyfluoride compounds from first principles

Multipole- and orbital-occupancies deduced from X-ray diffraction intensities by means of combined least-squaresand crystal field perturbation-calculations

Electronic properties of the two rutiles TiO₂ and VF₂: A comparative study

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Asphericity effects in the electron density of VF2

Cited by 5 publications

References 5 publications

Assessing exchange-correlation functional performance for structure and property predictions of oxyfluoride compounds from first principles

Assessing exchange-correlation functional performance for structure and property predictions of oxyfluoride compounds from first principles

Multipole- and orbital-occupancies deduced from X-ray diffraction intensities by means of combined least-squaresand crystal field perturbation-calculations

Electronic properties of the two rutiles TiO2 and VF2: A comparative study

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Asphericity effects in the electron density of VF₂

Electronic properties of the two rutiles TiO₂ and VF₂: A comparative study