A calculation of spectroscopic parameters for hydrogen fluoride with multi-reference state-specific coupled-cluster method

The multi-reference state-specific coupled-cluster method with a complete-active-space reference (CASCC) developed by our group has been used to calculate the potential energy curves, spectroscopic parameters, and vibrational levels for the ground ( X 1 Σ + ) and excited ( B 1 Σ + ) states of 19FH. The working algorithm for the CASCC method was derived with a computer-based automated approach that generates the CC energy and amplitude equations and the corresponding coupled-cluster diagrams. The spin–orbital sets for the CASCC calculations have been obtained using the complete-active-space self-consistent-field method (CASSCF). As determined by comparing the theoretical results with experimental ones reconstructed using the Rydberg–Klein–Reese method, the CASCC energies are better than those obtained with the CCSD and EOM-CCSD methods.