Investigating vibrational behavior in solution is crucial
for understanding
molecular dynamics within a solvent environment. Notably, the analysis
of Raman spectra for molecules in solution is important owing to its
ability to unveil intricate solute–solvent interactions. Previous
studies have effectively employed frequency calculations utilizing
the reference interaction site model self-consistent field method
in conjunction with constrained spatial electron density distribution
(RISM–SCF–cSED) to understand molecular vibrations in
solution, primarily focusing on fundamental vibrational modes. However,
the oversight of overtones and combination tones in these studies
prompted us to combine the vibrational self-consistent field (VSCF)
and vibrational second-order Mo̷ller–Plesset perturbation
(VMP2) methods with RISM–SCF–cSED to address these aspects
theoretically. Illustrating the efficacy of this integrated approach,
we computed the Raman spectra of sodium formate (NaHCOO) in water,
revealing the necessity of accounting for molecular anharmonicity
in solution vibrational analysis. Our findings underscore the potency
of VSCF and VMP2 in conjunction with RISM–SCF–cSED as
a robust theoretical framework for such calculations.