Correlation Energy of the Neon Atom

Abstract

The linked-cluster many-body perturbation theory has been applied in a calculation of the correlation energy of the neon atom in the ground state (${}_{}{}^1{}_{}{}^{}S$). The pair-correlation energy, obtained by summing the correlation energy between all pairs of states in the atom, is found to be - 0.413 26 a.u. About 5% of the pair-correlation energy comes from excitations to $g$, $h$, and $i$ states. Pair-pair interactions are found to be important and contribute 0.022 44 a.u. to the correlation energy. Correlation diagrams involving simultaneous excitations of three and more particles are found to be relatively unimportant and lead to a net contribution of only about 0.003 a.u. Our final value for the correlation energy is - 0.389 14 a.u., which is in excellent agreement with the nonrelativistic experimental correlation energy of - 0.389 a.u. A detailed comparison is made with the available configuration interaction calculations both with respect to numerical results as well as to the relative importance of various physical effects which contribute to the correlation energy.