Open-shell coupled-cluster theory for a general incomplete model space using eigenvalue-independent partitioning

Abstract

Multireference coupled-cluster (MRCC) theory using an eigenvalue-independent partitioning (EIP) technique is formulated for a general incomplete model space, taking a valence universal normal ordered wave operator …ifΩ = srmexp(S)s that acts upon the model space P. For the size-extensivity requirement the intermediate normalization is abandoned (i.e. PΩP ≠ P) and hence the closed part of Ω, Ω cl , is not unity. This leads to an implicit equation for the H eff. The EIP structure of the MRCC equation is capable of producing the main as well as the satellite states together.