Core-hole effect on dipolar and quadrupolar transitions of SrTiO3 and BaTiO3 at Ti K edge

Experimental pre-edge fine structures in the x-ray absorption spectra of SrTiO3 and BaTiO3 at Ti K edge are successfully reproduced within the framework of first-principles one-electron theory using the full-potential augmented plane wave plus local orbitals method. The importance of the following two points has been demonstrated: (1) proper inclusion of a Ti 1s core-hole using a large supercell, and (2) consideration of both dipolar and quadrupolar transitions. The core-hole effect is found to be more significant for quadrupolar transitions that form the first two peaks of the pre-edge structure, i.e., p1 to p2. They correspond to t2g and eg bands of the core-holed Ti. The other two peaks, p3 and p4, are found to be entirely due to the dipolar transition.