2020 年 61 巻 8 号 p. 1462-1467
We propose a new algorithm for numerical evaluation of x-ray absorption spectra based on the Green's function formalism in this paper. The method stands on the reduced-shifted conjugate-gradient (RSCG) method, which enables us to obtain the Green's functions with different energy-shifts simultaneously. The seed switching technique is combined into the RSCG method to improve the numerical accuracy and robustness of the algorithm, which we refer to the RSCG-SS method. The RSCG-SS method is applied for calculations of x-ray absorption spectra at the L2,3-edges of transition metals in simple oxides as a benchmark. The theoretical spectra obtained by the new algorithms are identical to those obtained by the full-diagonalization method following the Fermi's golden rule. The RSCG-SS method can also be applied for the calculation of spectra with a sizable Hamiltonian matrix (∼300,000) with reasonable computational costs.
