Determination of an improved set of harmonic force constants for benzene

The aim of this work is to describe a specific completely symmetrized, combined local mode/symmetrized modes (LM/SM), nonperturbative vibrational calculation procedure, and computer code, designed for implementation of large‐scale calculations on the vibrational energy levels in benzene C6H6, as well as its D6h isotopomers. Using this procedure and code, calculations have been performed on the fundamental frequencies of benzene, using the harmonic force constants, as well as a very small number of anharmonic constants, as adjustable input parameters. In this way, an improved set of symmetrized harmonic force constant values for benzene C6H6 have been determined, allowing for very good reproduction of the fundamental frequencies.