Correlated expansions ofn1Sandn3Sstates for two-electron atoms in exponential cosine screened potentials

Abstract

Two--electron atoms embedded in a plasma environment are studied with screened and exponential cosine screened Coulomb model potentials. Within a configuration interaction approach, and using parameter--free explicitly correlated basis functions, we have calculated the ground-state and first excited-state energies (and other mean values) for H${}^{\ensuremath{-}}$, He, and Li${}^{+}$. We analyze their evolution with the screening parameter and provide simple fits, which allow for practical and rapid evaluations for example in plasma applications.