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CATEGORIES:Theoretical Physics Seminars
SUMMARY:Exchange potentials in Kohn-Sham theory. - Nikitas
I. Gidopoulos Dept of Physics\, Durham University
DTSTART:20130918T130000Z
DTEND:20130918T150000Z
UID:TALK1190AT
URL:/talk/index/1190
DESCRIPTION:I shall present work which is a collaboration betw
een myself\, Tom Hollins and Stewart Clark from Du
rham University and Keith Refson from STFC.\n\nIn
this talk my intention is to rethink what we belie
ve we know about the Hartree-Fock (HF) approximati
on in the theory of electronic structure. I shall
present and discuss the results of a series of cal
culations. Conceptually\, these calculations are e
asy to understand: we calculate the HF ground stat
e Slater determinant (Phi) for a system and then w
e calculate the ground state single-particle densi
ty of Phi. Then\, we use a simple algorithm to "in
vert" the HF single-particle density in order to o
btain the local single-particle potential\, whose
ground state Slater determinant (different from Ph
i) has the same density as Phi.\nFinally\, we stud
y the band structure of this local potential for t
he various systems of interest.\n\nWe have applied
this method to a number of representative systems
where either the HF approximation or the common\,
local\, density functional theory (DFT) approxima
tions (or both) fail to give a qualitatively corre
ct band structure. For example\, HF predicts every
system to be insulating\, including simple metals
\, that are predicted to be semi-metallic. Typical
ly\, the lack of screening is thought to be cause
of this anomaly. Semi-conductors are also predicte
d to have a large gap. On the other hand\, common
approximations (LDA-GGA) in DFT are accurate for m
etals but predict too small band gaps for semi-con
ductors and also give too small or zero band gaps
for some transition-metal oxides that are antiferr
omagnetic insulators.\n\nWe will see that the meth
od gives a reasonably accurate description for all
these systems\, despite the fact that the underly
ing theoretical model is the HF approximation and
no correlation effects are included in the calcula
tions. (Defining correlation as whatever is added
beyond a HF calculation.) \nIn fact\, we exploit t
he benefit of treating exchange accurately\, but w
ith a local single-particle potential\, rather tha
n a non-local one.
LOCATION:Theory Library
CONTACT:Kevin Ralley
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