Multi-reference coupled-cluster study of the potential energy surface of the hydrogen fluoride dissociation including excited states

Multi-reference coupled-cluster calculations for the potential energy surface of the HF molecule including excited states are carried out. Using the multi-reference exponential wavefunction [M. Hanrath, J. Chem. Phys. 123 (2005) 84102] and the single-reference formalism based multi-reference coupled-cluster ansatz [J. Chem. Phys. 94 (1991) 1229, J. Chem. Phys. 99 (1993) 1875] the results are analyzed and discussed with respect to full CI results. The present work completes previous studies which considered calculations with partially restricted residual equations only. A certain attention is paid to spatial degeneracy issues.