532 research outputs found
NMR shieldings from density functional perturbation theory: GIPAW versus all-electron calculations
We present a benchmark of the density functional linear response calculation
of NMR shieldings within the Gauge-Including Projector-Augmented-Wave method
against all-electron Augmented-Plane-Wavelocal-orbital and uncontracted
Gaussian basis set results for NMR shieldings in molecular and solid state
systems. In general, excellent agreement between the aforementioned methods is
obtained. Scalar relativistic effects are shown to be quite large for nuclei in
molecules in the deshielded limit. The small component makes up a substantial
part of the relativistic corrections.Comment: 3 figures, supplementary material include
The shortcomings of semi-local and hybrid functionals: what we can learn from surface science studies
A study of the adsorption of CO on late 4d and transition metal (111)
surfaces (Ru, Rh, Pd, Ag, Os, Ir, and Pt) considering atop and hollow site
adsorption is presented. The applied functionals include the gradient corrected
PBE and BLYP functional, and the corresponding hybrid Hartree-Fock density
functionals HSE and B3LYP. We find that PBE based hybrid functionals
(specifically HSE) yield, with the exception of Pt, the correct site order on
all considered metals, but they also considerably overestimate the adsorption
energies compared to experiment. On the other hand, the semi-local BLYP
functional and the corresponding hybrid functional B3LYP yield very
satisfactory adsorption energies and the correct adsorption site for all
surfaces. We are thus faced with a Procrustean problem: the B3LYP and BLYP
functionals seem to be the overall best choice for describing adsorption on
metal surfaces, but they simultaneously fail to account well for the properties
of the metal, vastly overestimating the equilibrium volume and underestimating
the atomization energies. Setting out from these observations, general
conclusions are drawn on the relative merits and drawbacks of various
semi-local and hybrid functionals. The discussion includes a revised version of
the PBE functional specifically optimized for bulk properties and surface
energies (PBEsol), a revised version of the PBE functional specifically
optimized to predict accurate adsorption energies (rPBE), as well as the
aforementioned BLYP functional. We conclude that no semi-local functional is
capable to describe all aspects properly, and including non-local exchange also
only improves some, but worsens other properties.Comment: 12 pages, 6 figures; to be published in New Journal of Physic
Maximally localized Wannier functions in LaMnO3 within PBE+U, hybrid functionals, and partially self-consistent GW: an efficient route to construct ab-initio tight-binding parameters for e_g perovskites
Using the newly developed VASP2WANNIER90 interface we have constructed
maximally localized Wannier functions (MLWFs) for the e_g states of the
prototypical Jahn-Teller magnetic perovskite LaMnO3 at different levels of
approximation for the exchange-correlation kernel. These include conventional
density functional theory (DFT) with and without additional on-site Hubbard U
term, hybrid-DFT, and partially self-consistent GW. By suitably mapping the
MLWFs onto an effective e_g tight-binding (TB) Hamiltonian we have computed a
complete set of TB parameters which should serve as guidance for more elaborate
treatments of correlation effects in effective Hamiltonian-based approaches.
The method-dependent changes of the calculated TB parameters and their
interplay with the electron-electron (el-el) interaction term are discussed and
interpreted. We discuss two alternative model parameterizations: one in which
the effects of the el-el interaction are implicitly incorporated in the
otherwise "noninteracting" TB parameters, and a second where we include an
explicit mean-field el-el interaction term in the TB Hamiltonian. Both models
yield a set of tabulated TB parameters which provide the band dispersion in
excellent agreement with the underlying ab initio and MLWF bands.Comment: 30 pages, 7 figure
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