Li 2 ground and excited states by the open-shell coupled-cluster method

Abstract

The open-shell coupled-cluster method is used to calculate the potential functions of the nine lowest states of Li 2, at internuclear separation of 4⩽ R⩽11 bohr, with a 74-function contracted-Gaussian basis. The usual complete-model-space calculation diverges, and a general, incomplete model space is used. Excellent agreement is obtained with experimentally known molecular constants: equilibrium internuclear separations are accurate to 0.01 Å, dissociation and excitation energies to 0.02 eV, and vibrational constants to 3 cm −1. Possible difficulties in model space structure are discussed.