6 research outputs found
Frozen local hole approximation
The frozen local hole approximation (FLHA) is an adiabatic approximation
which is aimed to simplify the correlation calculations of valence and
conduction bands of solids and polymers. Within this approximation correlated
local hole states (CLHSs) are explicitely generated by correlating local
Hartree-Fock (HF) hole states. The hole orbital and its occupancy is kept
frozen during these correlation calculations. Effective Hamilton matrix
elements are then evaluated with the above CLHSs; diagonalization finally
yields the desired correlation corrections for the cationic hole states. We
compare and analyze the results of the FLHA with the results of a full MRCI(SD)
(multi-reference configuration interaction with single and double excitations)
calculation for two prototype model systems, (H2)n ladders and H-(Be)n-H
chains. Excellent numerical agreement between the two approaches is found.
Comparing the FLHA with a full correlation treatment in the framework of
quasi-degenerate variational perturbation theory reveals that the leading
contributions in the two approaches are identical. Thus, the FLHA is
well-justified and provides a very promising and efficient alternative to fully
correlated wavefunction-based treatments of the valence and conduction bands in
extended systems.Comment: RevTeX, 9 pages, 7 figures (6 ps files
Multireference configuration interaction treatment of excited-state electron correlation in periodic systems: the band structure of trans-polyacetylene
A systematic method to account for electron correlation in periodic systems
which can predict quantitatively correct band structures of non-conducting
solids from first principles is presented. Using localized Hartree-Fock
orbitals (both occupied and virtual ones), an effective Hamiltonian is built up
whose matrix elements can easily be transferred from finite to infinite
systems. To describe the correlation effects wave-function-based multireference
configuration interaction (MRCI) calculations with singly and doubly excited
configurations are performed. This way it is possible to generate, both,
valence and conduction bands with all correlation effects taken into account.
Trans-polyacetylene is chosen as a test system.Comment: 9 pages, 2 figures, submitted to Chem. Phys. Let
Ab initio Green's function formalism for band structures
Using the Green's function formalism, an ab initio theory for band structures
of crystals is derived starting from the Hartree-Fock approximation. It is
based on the algebraic diagrammatic construction scheme for the self-energy
which is formulated for crystal orbitals (CO-ADC). In this approach, the poles
of the Green's function are determined by solving a suitable Hermitian
eigenvalue problem. The method is not only applicable to the outer valence and
conduction bands, it is also stable for inner valence bands where strong
electron correlations are effective. The key to the proposed scheme is to
evaluate the self-energy in terms of Wannier orbitals before transforming it to
a crystal momentum representation. Exploiting the fact that electron
correlations are mainly local, one can truncate the lattice summations by an
appropriate configuration selection scheme. This yields a flat configuration
space; i.e., its size scales only linearly with the number of atoms per unit
cell for large systems and, under certain conditions, the computational effort
to determine band structures also scales linearly. As a first application of
the new formalism, a lithium fluoride crystal has been chosen. A minimal basis
set description is studied, and a satisfactory agreement with previous
theoretical and experimental results for the fundamental band gap and the width
of the F 2p valence band complex is obtained.Comment: 20 pages, 3 figures, 1 table, RevTeX4, new section on lithium
fluorid
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