First-principles multielectron calculations of Ni L2,3 NEXAFS and ELNES for LiNiO2 and related compounds -: art. no. 075123

A technique to compute 3d transition-metal L-2,L-3-edge near-edge x-ray-absorption fine structure (NEXAFS) and electron energy-loss near-edge structure (ELNES) is adopted to predict and interpret spectra from NiO, LiNiO2, and NiO2. Multielectron wave functions were obtained as a linear combination of Slater determinants. The Slater determinants were constructed using all Ni-2p- and Ni-3d-based molecular orbitals, instead of atomic orbitals, obtained by solving the Dirac equation within the local density approximation for NiO6m- clusters (m=10, 9, and 8). The O-2p contributions through covalency can therefore be included automatically without any other scheme. Experimental ELNES for the three compounds were satisfactory reproduced by the present calculations, which unambiguously shows that Ni atoms are Ni(III) with a low-spin state in LiNiO2, and Ni(IV) with a low-spin state in NiO2. The origin of satellite peaks in the spectra is also clarified. The present method is based on the robust multielectron quantum theory, which could be applied to the analysis and prediction of L-2,L-3-edge spectra of other transition-metal compounds.