The open-shell coupled-cluster method in general model space: Five states of LiH

The open-shell coupled-cluster method is used to calculate the potential functions of the five lowest states of LiH, at internuclear separation of 2.0≤R≤10.0 bohr, with a 18σ9π2δ basis. The usual complete-model-space calculation diverges, and a general, incomplete model space, comprising the physically important 2σ 2, 2σ3σ, and 2σ1π configurations (but excluding the high-energy determinants 3σ 2 and 1π 2 from the P space) is used. Good agreement with experimental molecular constants is obtained.