Structure, polarity, dynamics, and vibrational spectral diffusion of liquid–vapour interface of a water–methanol mixture from first principles simulation using dispersion corrected density functional

The effects of dispersion interaction on the structural, dipolar and dynamical properties of liquid–vapour interface of an aqueous solution of methanol have been investigated through first principles simulations. A description of structural properties including the inhomogeneous density profiles of molecules, hydrogen bond distributions and orientational profiles are presented in detail. Among the dynamical properties, diffusion, orientational relaxation, hydrogen bond dynamics and vibrational spectral diffusion of molecules are determined. The variation of the polarity of the molecules from bulk to the interface are also calculated. The current first principles simulation results are compared with the results of dispersion uncorrected study. The dispersion corrected study predicts an increase in the number of molecules in their neighborhood, which are held together by non-hydrogen-bonded dispersion interactions. This results in the faster relaxation of hydrogen bonds, diffusion and rotational motion of molecules in comparison to the dispersion uncorrected study. Furthermore, the effects of dispersion correction on the dynamics of vibrational frequency fluctuations are emphasized, which clearly captures the dynamics of hydrogen bond fluctuations in the respective regions.