Elimination of translational and rotational motions in nuclear orbital plus molecular orbital theory: Contribution of the first-order rovibration coupling

The translation- and rotation-free nuclear orbital plus molecular orbital (TRF-NOMO) theory was developed to determine nonadiabatic nuclear and electronic wave functions. This study implemented a computational program for the TRF-NOMO method including first-order rotational terms, which corresponds to rovibronic coupling. Numerical assessments of first-order TRF-NOMO Hartree-Fock as well as second-order Møller-Plesset perturbation methods were carried out for several small molecules. The first-order contributions give small corrections in energy. Thus, we confirm that the approximate zeroth-order treatment is sufficient for eliminating the rotational contamination.