Molecular dynamic simulations of terahertz spectra for water-methanol mixtures

Abstract

Molecular dynamic (MD) simulations have been performed to probe the single molecule and collective dynamics in water–methanol mixtures. The MD simulations were carried out for mixtures with 0.0, 0.12, 0.21, 0.5 and 1.0 mol fraction of methanol at the temperature 298 K. Both translational and rotational densities of states for water and methanol molecules in the far infrared (IR) region are reported. A new method for the identification of discrete dielectric relaxation modes in molecular liquids is described. The method is based on the decomposition of autocorrelation functions (ACFs) in the time domain and enables one to obtain the distribution of characteristic times. In this work, the technique was applied to the dipole moment time ACFs for water–methanol mixtures, and the distributions of dielectric relaxation times are reported. Several distinct relaxation modes in the dielectric spectra of the mixtures are identified and the origin of composite (anomalous) dielectric spectra is discussed.

Keywords:

• dielectric relaxation
• microwave
• far-infrared
• molecular dynamics simulations
• water–methanol mixtures

Acknowledgement

The authors are grateful for the financial support of the Russian Foundation for Basic Research through the research grant 08-03-00095.