Computer- aided implementation if multireference coupled cluster methods.

Abstract: The aim of this project is to generalize the tool for computer-aided implementation of coupled-cluster (CC) and perturbation theory methods, called Tensor Contraction Engine (TCE), to Hilbert-space multireference (MR) methods based on multiple Fermi vacua. So far, this tool has only been used for single-reference methods,or for Fock space MR methods, which can be formulated with respect to a single Fermi vacuum. Generalization of this tool should greatly facilitate further development of Hilbert-space multireference CC methods. For example, the tedious coding of effective Hamiltonian matrix elements between mutually tri- and tetra- excited references, renormalization terms in the Jeziorski-Monkhorst or Mukherjee MRCC approaches when including triexcitations in the cluster operator, etc., should be to a big extent automatized. Moreover, TCE generates code which employs point group symmetry and is parallelized.