Molecular dynamics study of the liquid-vapor interface of acetonitrile: equilibrium and dynamical properties.

The equilibrium and dynamical properties of the liquid-vapor interface of pure acetonitrile are studied by means of molecular dynamics simulations. Both nonpolarizable and polarizable models are employed in the present study. For the nonpolarizable model, the simulations are carried out for two different system sizes and at two different temperatures whereas the simulation with the polarizable model is done for a single system. The inhomogeneous density, anisotropic orientational profile, the width of the interface, and also the surface tension are calculated at room temperature and also at a lower temperature of 273 K. The dynamical aspects of the interface are investigated in terms of the single-particle dynamical properties such as the relaxation of velocity autocorrelation and the translational diffusion coefficients along the perpendicular and parallel directions and the dipole orientational relaxation of the interfacial acetonitrile molecules. The results of the interfacial dynamics are compared with those of the corresponding bulk phases at both temperatures. The convergence of the calculated results with respect to the length of simulation runs and the system size are also discussed.