Ab initio molecular dynamics study of liquid methanol.pdf

a r X i v : p h y s i c s / 0 2 1 0 1 2 3 v 1 [ p h y s i c s .c h e m - p h ] 2 9 O c t 2 0 0 2 Ab initio molecular dynamics study of liquid methanol Jan-Willem Handgraaf, Titus S. van Erp, and Evert Jan Meijer Department of Chemical Engineering, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV AMSTERDAM, The Netherlands Fax: +31-20-5255604, email: ejmeijer@science.uva.nl Abstract We present a density-functional theory based molecular-dynamics study of the struc- tural, dynamical, and electronic properties of liquid methanol under ambient condi- tions. The calculated radial distribution functions involving the oxygen and hydroxyl hydrogen show a pronounced hydrogen bonding and compare well with recent neu- tron diffraction data, except for an underestimate of the oxygen-oxygen correlation. We observe that, in line with infrared spectroscopic data, the hydroxyl stretching mode is significantly red-shifted in the liquid. A substantial enhancement of the dipole moment is accompanied by significant fluctuations due to thermal motion. Our results provide valuable data for improvement of empirical potentials. 1. Introduction Liquid methanol is of fundamental interest in natural sciences and of signifi- cant importance in technical and industrial applications. The liquid phase of the simplest alcohol is widely studied, both experimentally and theoretically. Among the alcohols, methanol is the closest analog to water. The character- istic hydroxyl group allows methanol to form hydrogen bonds that dominate the structural and dynamical behavior of the liquid phase. The methyl group does not participate in the hydrogen bonding and constitutes the distinction with water. This difference is apparent in the microscopic structure of the liq- uid, with water having a tetrahedral-like coordination, whereas for methanol experiments and molecular simulation suggest a local structure consisting of chains, rings, or small clusters. The precise quantification of the mic