COUPLED-CLUSTER BASED LINEAR-RESPONSE APPROACH TO PROPERTY CALCULATIONS - DYNAMIC POLARIZABILITY AND ITS STATIC LIMIT

In this paper is described in detail a time-independent version of the coupled-cluster based linear response theory (CC-LRT) for computing s econd-order molecular properties. It utilizes a coupled-cluster repres entation of both the ket and bra functions for the ground state that a re conjugates of each other, while for representing the excited functi ons-which enter the spectral representation of the response function-i t employs coupled-cluster based ansatz which generate ket and bra exci ted functions that are bi-orthogonal to each other as well as to the c orresponding ground state functions. Emphasis has been given to the im portant practical problem of avoiding the tedious sum-over-state formu la for second-order properties such as the dynamic polarizability by w ay of implicitly inverting a dressed Hamiltonian matrix in a set of el ementary bi-orthogonal bases which are much simpler than those represe nting eigenvectors for the excited states. It is shown that the elemen tary bi-orthogonal bases used for the excited space in our formulation respect strict orthogonality with the ground state function even for the truncated, approximate version of CC-LRT. It is also proven that t he theory generates size-extensive as well as size-consistent values o f the dynamic polarizability for a closed-shell system that is compose d of noninteracting closed-shell subsystems. As numerical applications , the first results using this formalism are reported for LiH, BeH+, H F, H2O, HCl, and H2S.