Progress in the quantum description of vibrational motion of polyatomic molecules

Publisher Summary This chapter reviews the progress in the quantum description of the vibrational motion of polyatomic molecules, with a focus on developments made in the code MULTIMODE’ (MM). Following a brief historical perspective of the use of normal modes in vibrational analysis it shows how this approach has been extended to provide a computationally powerful approach to accurately describe the vibrations of fairly large molecules. The approach is based on an exact Hamiltonian in normal coordinates, a general n-mode representation of the full potential, and the implementation of vibrational self-consistent field/configuration interaction methods. Several case studies are presented based on the Single-Reference (SR) version of MM. Following that it describes a major generalization of MM that blends the key aspects of MM-SR with the Reaction Path Hamiltonian. This version is illustrated for the fluxional complex (OHˉ)H 2 O. It has been concluded with a critical examination of the current bottlenecks in the computational approach and prospects for future progress.