Core-excitation effects on atomic transitions

By including explicitly the electronic configurations with three simultaneously excited electronic orbitals, we have successfully extended the BSCI (B-spline based configuration interaction) method to estimate directly the effects of inner shell core-excitation to atomic transitions. In particular, we are able to carry out detailed ab initio investigation on the core polarization effects without the use of parameterized model potential. We investigate in detail quantitatively the change in atomic transition rate due to the core-excitations for four-electron systems, especially for transitions involving double excited states and those with small oscillator strengths. Quantitatively, for the Be-like systems, we are able to achieve an agreement between the length and velocity results to better than 1% for most transitions. Applications to neutral Carbon also demonstrate the effectiveness of the extended BSCI methods to treat explicitly the core-excitation in atomic transitions. A typical extended BSCI calculation requires substantially more computational effort than other L2 methods. It can only be carried out under the parallel computing environment. With the ongoing hardware upgrading from 32-bit to 64-bit computing environment, we anticipate a more comprehensive extended BSCI study on Carbon-like ions and heavier atomic systems with 2 closed shells such as Si-like ions in coming years.