Quasiharmonic Vibrations of Water, Water Dimer, and Liquid Water from Principal Component Analysis of Quantum or QM/MM Trajectories

Beyond the harmonic approximation: Traditional methods of calculating molecular vibrations based on Wilson's FG matrices have remained unchanged for more than half a century. Condensed-phase molecular vibrations require moving beyond the harmonic approximation. The authors test a new approach to calculating molecular vibrations based on statistical analysis of atomic configurations that sample the underlying quantum mechanical energy surface (see graphic).