Applications of core-valence extensive multi-reference coupled cluster theory and core-extensive coupled cluster-based linear response theory

The single reference coupled cluster based linear response theory (CCLRT) and valence-universal multi-reference coupled cluster (VU-MRCC) theory for direct difference energy calculations have been presented. The similarities and differences in the structure of these two formalisms have also been addressed. The core-extensive CCLRT is applied to compute the ionization potentials (IPs) of HCl and excitation energies of CuH using Hartree-Fock (HF) orbitals. We further report the relativistic applications of the VU-MRCC theory through the computation of the ground and excited/ionized state energies and related properties of Ag and Hg atoms using Dirac-Hartree-Fock (DHF) orbitals. The IPs, excitation energies, and the spectroscopic constants reported here are in favorable agreement with experiment and with other correlated calculations.