A priori calculation of atomic oscillator strengths using correlated transition states

Atomic oscillator strengths (length and velocity forms) are calculated for a series of transitions using transition Hamiltonians within the Hartree-Fock (HF) approximation. Two methods are implemented: the first defines a transition configuration (TC) corresponding to an average over the occupation numbers of initial and final configurations of the transition considered; the second defines a transition state (TS) corresponding to an average over the energies of the states involved in the transition. In general the TS results agree well with the corresponding HF values, while the TC results show larger discrepancies due to nonphysical self-interactions described in the text. An original method is described for obtaining a multiconfigurational transition state wavefunction. This method (MCTS) is applied to the evaluation of the oscillator strength of the transition Be(1s 2 2s 2 1 S to 1s 2 2s2p 1 P degrees ).