86 research outputs found
A study of transition metal K-edge x-ray absorption spectra of LaBO3 (B=Mn, Fe, Co, Ni), La2CuO4 and SrMnO3 using partial density of states
The transition metal K-edge x-ray absorption near edge structure (XANES)
studies have been carried on LaBO3 (B=Mn, Fe, Co, Ni), La2CuO4 and SrMnO3
compounds. The theoretical spectra have been calculated using transition metal
(TM) 4p density of states (DOS) obtained from full-potential LMTO density
functional theory. The exchange-correlation functional used in this calculation
is taken under local density approximation (LDA). The comparison of
experimental spectra with the calculated ones indicates that single-particle
transitions under LDA are sufficient to generate all the observed XANES
including those which have earlier been attributed to many-body shake-up
transitions and core-hole potentials. The present study reveals that all the
experimentally observed features are mainly due to distribution in TM 4p DOS
influenced by hybridization with other orbitals. Specifically, for LaMnO3, the
feature earlier attributed to shake-up process is seen to arise from
hybridization of Mn 4p with La 6p and O 2p orbitals; in La2CuO4 the features
attributed to core hole potential correspond to hybridization of Cu 4p with La
6p, La 5d and O 2p orbitals. To see the effect of inhomogeneous electronic
charge distribution and on-site Coulomb and exchange interaction (U) on the
XANES of these compounds generalized-gradient approximation and U corrections
are incorporated in the calculations. These corrections do not generate any new
features in the spectra but affect the detailed intensity and positions of some
of the features.Comment: 23 pages, 8 figures. To appear in J. Phys.: Condens. Matte
X-ray Absorption Near-Edge Structure calculations with pseudopotentials. Application to K-edge in diamond and alpha-quartz
We present a reciprocal-space pseudopotential scheme for calculating X-ray
absorption near-edge structure (XANES) spectra. The scheme incorporates a
recursive method to compute absorption cross section as a continued fraction.
The continued fraction formulation of absorption is advantageous in that it
permits the treatment of core-hole interaction through large supercells
(hundreds of atoms). The method is compared with recently developed
Bethe-Salpeter approach. The method is applied to the carbon K-edge in diamond
and to the silicon and oxygen K-edges in alpha-quartz for which polarized XANES
spectra were measured. Core-hole effects are investigated by varying the size
of the supercell, thus leading to information similar to that obtained from
cluster size analysis usually performed within multiple scattering
calculations.Comment: 11 pages, 4 figure
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