First principles molecular orbital calculations of three titanium oxides are made in order to quantify the absolute transition energies of ELNES/NEXAFS at the O K and Ti L2,3 edges and to clarify the origin of their chemical shifts. The absolute transition energies as well as their chemical shifts at two edges are satisfactorily reproduced using clusters composed of 24 to 63 atoms when Slater's transition state method is employed allowing temporary spin-polarization. The O K edge shows a positive shift with the increase of the formal number of d electrons per Ti ion. The shift can be mainly ascribed to the variation of the energy of the t2g-like band, although the energy of the O 1s core-orbital varies slightly. On the other hand, the Ti L2,3 edge shows negative shift, which is found to be explained by the balance of energies of the Ti 2p and the t2g-like band. The magnitude of the chemical shifts is not significantly altered by the manner of the octahedral linkage.
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