An efficient method for calculating molecular radiative intensities in the VUV and soft X-ray wavelength regions

An efficient method for calculating intensities of molecular radiative transitions in the vacuum UV and soft X-ray wavelength regions using MCSCF wave functions is presented. The initial and final states are expanded within large configurational spaces and separately optimized with sets of molecular orbitals that are mutually non-orthogonal. An optimal construction of the transition density matrix is achieved through a sorting algorithm of the symbolic configuration elements in conjunction with the biorthogonalization technique of Malmqvist [1] for transforming the molecular orbitals. The performance of the method is demonstrated for the soft X-ray emission spectra of CO and N₂.