Four-Reference State-Specific Brillouin-Wigner Coupled-Cluster Method: Study of the IBr Molecule

Abstract

We implemented the state-specific Brillouin–Wigner coupled-cluster method for the complete model space spanned by four reference configurations generated by two electrons in two active orbitals. We applied the method (together with the previously suggested a posteriori size-extensivity correction) to the calculation of spectroscopic constants of the IBr molecule, using averaged relativistic effective core potential.

Keywords

• Potential curve
• spectroscopic constants of IBr
• multireference coupled clusters
• state-specific methods
• size extensivity
• Brillouin–Wigner perturbation theory
• intruder states