2,989 research outputs found
Spectral density and metal-insulator phase transition in Mott insulators within RDMFT
We present a method for calculating the spectrum of periodic solids within
reduced density matrix functional theory. This method is validated by a
detailed comparison of the angular momentum projected spectral density with
that of well established many-body techniques, in all cases finding an
excellent agreement. The physics behind the pressure induced insulator-metal
phase transition in MnO is investigated. The driving mechanism of this
transition is identified as increased crystal field splitting with pressure,
resulting in a charge redistribution between the Mn and symmetry
projected states.Comment: arXiv admin note: text overlap with arXiv:0912.111
The generalized gradient approximation kernel in time-dependent density functional theory
A complete understanding of a material requires both knowledge of the excited
states as well as of the ground state. In particular, the low energy
excitations are of utmost importance while studying the electronic, magnetic,
dynamical, and thermodynamical properties of the material. Time-Dependent
Density Functional Theory (TDDFT), within the linear regime, is a successful
\textit{ab-initio} method to access the electronic charge and spin excitations.
However, it requires an approximation to the exchange-correlation (XC) kernel
which encapsulates the effect of electron-electron interactions in the
many-body system. In this work we derive and implement the spin-polarized XC
kernel for semi-local approximations such as the adiabatic Generalized Gradient
Approximation (AGGA). This kernel has a quadratic dependence on the wavevector,
{\bf q}, of the perturbation, however the impact of this on the electron energy
loss spectra (EELS) is small. Although the GGA functional is good in predicting
structural properties, it generality overestimates the exchange spin-splitting.
This leads to higher magnon energies, as compared to both ALDA and experiment.
In addition, interaction with the Stoner spin-flip continuum is enhanced by
AGGA, which strongly suppresses the intensity of spin-waves.Comment: 11 pages, 7 figure
All-electron Exact Exchange Treatment of Semiconductors: Effect of Core-valence Interaction on Band-gap and -band Position
Exact exchange (EXX) Kohn-Sham calculations within an all-electron
full-potential method are performed on a range of semiconductors and insulators
(Ge, GaAs, CdS, Si, ZnS, C, BN, Ne, Ar, Kr and Xe). We find that the band-gaps
are not as close to experiment as those obtained from previous pseudopotential
EXX calculations. Full-potential band-gaps are also not significantly better
for semiconductors than for insulators, as had been found for
pseudopotentials. The locations of -band states, determined using the
full-potential EXX method, are in excellent agreement with experiment,
irrespective of whether these states are core, semi-core or valence. We
conclude that the inclusion of the core-valence interaction is necessary for
accurate determination of EXX Kohn-Sham band structures, indicating a possible
deficiency in pseudopotential calculations.Comment: 4 pages 2 fig
Reduced Density Matrix Functional for Many-Electron Systems
Reduced density matrix functional theory for the case of solids is presented
and a new exchange correlation functional based on a fractional power of the
density matrix is introduced. We show that compared to other functionals, this
produces more accurate results for both finite systems. Moreover, it captures
the correct band gap behavior for conventional semiconductors as well as
strongly correlated Mott insulators, where a gap is obtained in absence of any
magnetic ordering.Comment: 4 figs and 1 tabl
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