67 research outputs found
Ab initio study of MF2 (M=Mn, Fe, Co, Ni) rutile-type compounds using the periodic unrestricted Hartree-Fock approach
The ab initio periodic unrestricted Hartree-Fock method has been applied in the investigation of the ground-state structural, electronic, and magnetic properties of the rutile-type compounds MF2 (M=Mn, Fe, Co, and Ni). All electron Gaussian basis sets have been used. The systems turn out to be large band-gap antiferromagnetic insulators; the optimized geometrical parameters are in good agreement with experiment. The calculated most stable electronic state shows an antiferromagnetic order in agreement with that resulting from neutron scattering experiments. The magnetic coupling constants between nearest-neighbor magnetic ions along the [001], [111], and [100] (or [010]) directions have been calculated using several supercells. The resulting ab initio magnetic coupling constants are reasonably satisfactory when compared with available experimental data. The importance of the Jahn-Teller effect in FeF2 and CoF2 is also discussed
Calculation of the vibration frequencies of alpha-quartz: The effect of Hamiltonian and basis set
Comment on "Accurate Hartree-Fock energy of extended systems using large Gaussian basis sets"
Combining the Hybrid Functional Method with Dynamical Mean-Field Theory
We present a new method to compute the electronic structure of correlated
materials combining the hybrid functional method with the dynamical mean-field
theory. As a test example of the method we study cerium sesquioxide, a strongly
correlated Mott-band insulator. The hybrid functional part improves the
magnitude of the pd-band gap which is underestimated in the standard
approximations to density functional theory while the dynamical mean-field
theory part splits the 4f-electron spectra into a lower and an upper Hubbard
band.Comment: 5 pages, 2 figures, replaced with revised version, published in
Europhys. Let
Wave-function-based approach to quasiparticle bands: new insight into the electronic structure of c-ZnS
Ab initio wave-function-based methods are employed for the study of
quasiparticle energy bands of zinc-blende ZnS, with focus on the Zn 3d
"semicore" states. The relative energies of these states with respect to the
top of the S 3p valence bands appear to be poorly described as compared to
experimental values not only within the local density approximation (LDA), but
also when many-body corrections within the GW approximation are applied to the
LDA or LDA+U mean-field solutions [T. Miyake, P. Zhang, M. L. Cohen, and S. G.
Louie, Phys. Rev. B 74, 245213 (2006)]. In the present study, we show that for
the accurate description of the Zn 3d states a correlation treatment based on
wave function methods is needed. Our study rests on a local Hamiltonian
approach which rigorously describes the short-range polarization and charge
redistribution effects around an extra hole or electron placed into the valence
respective conduction bands of semiconductors and insulators. The method also
facilitates the computation of electron correlation effects beyond relaxation
and polarization. The electron correlation treatment is performed on finite
clusters cut off the infinite system. The formalism makes use of localized
Wannier functions and embedding potentials derived explicitly from prior
periodic Hartree-Fock calculations. The on-site and nearest-neighbor charge
relaxation lead to corrections of several eV to the Hartree-Fock band energies
and gap. Corrections due to long-range polarization are of the order of 1.0 eV.
The dispersion of the Hartree-Fock bands is only little affected by electron
correlations. We find the Zn 3d "semicore" states to lie about 9.0 eV below the
top of the S 3p valence bands, in very good agreement with values from
valence-band x-ray photoemission.Comment: 44 pages, 8 figures, submitted to Phys. Rev.
Calculations of nickel band structure and adsorption on nickel thin films, using an extension of the CNDO formalism
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