title: Vibrational spectrum at a water surface: a hybrid quantum mechanics/molecular mechanics molecular dynamics approach.
abstract: A hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulation is applied to the calculation of surface orientational structure and vibrational spectrum (second-order nonlinear susceptibility) at the vapor/water interface for the first time. The surface orientational structure of the QM water molecules is consistent with the previous MD studies, and the calculated susceptibility reproduces the experimentally reported one, supporting the previous results using the classical force field MD simulation. The present QM/MM MD simulation also demonstrates that the positive sign of the imaginary part of the second-order nonlinear susceptibility at the lower hydrogen bonding OH frequency region originates not from individual molecular orientational structure, but from cooperative electronic structure through the hydrogen bonding network.
authors.affiliation: Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan. ishiyama@m.tohoku.ac.jp
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Ishiyama
authors.forename: Hideaki
authors.initials: H
authors.lastname: Takahashi
authors.forename: Akihiro
authors.initials: A
authors.lastname: Morita
mesh_terms: D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D011336:Probability; D011789:Quantum Theory; D013057:Spectrum Analysis; D014732:Vibration; D014835:Volatilization; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water