Can a single-reference approach provide a balanced description of ground and excited states? A comparison of the completely renormalized equation-of-motion coupled-cluster method with multireference quasidenegenerate perturbation theory near a conical intersection and along a photodissociation coordinate in ammonia

The two lowest electronically adiabatic potential energy surface of ammonia in the region of the conical interaction and at a sequence of geometries are calculated by employing a multireference (MR) method and a single-reference (SR) method. The MR calculations are based on multiconfiguration quasigenerated perturbation theory and the SR calculations, carried out with the same basis, employ completely renormalized equation-of-motion coupled-cluster method with single and double and a noniterative treatment of triples.