Resolution of Velocity Autocorrelation Function of a Model Liquid

The velocity autocorrelation function (VAF) of a soft-core model liquid whose state is close to a freezing point is resolved into several basic modes by the method of an autoregressive analysis. The results show that a pure Langevin process does not inhere in the process of diffusion and that the motion of an atom of a classical monatomic liquid is described by the superposition of more than two different damped cosine modes. No clear-cut distinction is observed between diffusive and oscillatory motions. Those structures observed in the VAF and in spectrum are clearly explained by using the resolved modes.