1201.6154 (Dm. Korotin et al.)

Electronic correlations and crystal structure distortions in BaBiO3    [PDF]

Dm. Korotin, V. Kukolev, A. V. Kozhevnikov, D. Novoselov, V. I. Anisimov

BaBiO3 is a material where formally Bi 4+ ions with half-filled 6s-states
form an alternating set of Bi 3+ and Bi 5+ ions resulting in a charge ordered
insulator. Charge ordering is accompanied by a breathing distortion of BiO6
octahedra (extension and contraction of Bi-O bond lengths). Standard Density
Functional Theory (DFT) calculations are unable to obtain crystal structure
instability due to pure breathing distortions. Combined effect of breathing
distortions and tilting of BiO6 octahedra allows DFT to reproduce qualitatively
experimentally observed insulator with monoclinic crystal structure but gives
strong underestimation of breathing distortion parameter and energy gap value.
In the present work we revert to the BaBiO3 problem with GGA+U method using
Wannier functions basis set for Bi 6s-band. Due to high oxidation state of
bismuth in this material Bi 6s-symmetry Wannier function is predominantly
extended spatially on surrounding oxygen ions and hence differs strongly from
pure atomic 6s-orbital. That is in sharp contrast to transition metal oxides
(with exclusion of high oxidation state compounds) where a major part of d-band
Wannier function is concentrated on metal ion and pure atomic d-orbital can
serve as a good approximation. GGA+U calculation not only gave very good
agreement between calculated and experimental monoclinic crystal structure
parameters and energy gap values. It has reproduced successfully crystal
structure instability due to pure breathing distortions without octahedra
tilting. Such instability could be a reason for phonon softening in hole doped
cubic Ba{1-x}K{x}BiO3.

View original: http://arxiv.org/abs/1201.6154