The precision of the mixed configuration-interaction plus many-body-perturbation-theory (CI+MBPT) method is limited in multivalence atoms by the large size of valence CI space. Previously, to study this problem, the CI+MBPT method was applied to calculations of energies in a four-valence electron atom, Si i. It was found that by using a relatively small cavity of 30 a.u. and by choosing carefully the configuration space, quite accurate agreement between theory and experiment at the level of $100 {\text{cm}}^{-1}$ can be obtained, especially after subtraction of systematic shifts for groups of states of the same $J$ and parity. However, other properties are also important to investigate. In this work, the CI+MBPT method is applied to studies of transition probabilities, oscillator strengths, and lifetimes. A close agreement with accurate experimental measurements and other elaborate theories is obtained. The long-term goal is to extend the CI+MBPT approach to applications in more complex atoms, such as lantanides and actinides.

• Received 22 December 2015

DOI:https://doi.org/10.1103/PhysRevA.93.022511