Ethanol force fields:: A molecular dynamics study of polarization effects on different phases

We have studied two simple approaches to consider thermodynamic state dependent electrostatic interactions for molecular modeling of different phases of ethanol: the addition of an isotropic point polarizability located in the oxygen, and a self-consistent calculation of the effective dipole moment at each thermodynamic state. We have performed molecular dynamics simulations in order to investigate the thermodynamic properties, structure and dynamics of the liquid phase at three experimental densities, as well as in the monoclinic crystal and at critical conditions. In order to rationalize the effects of changing the dipole moment of the molecules, simulations with a nonpolarizable model for ethanol were also performed. The results show that a nonpolarizable model with an effective dipole moment is able to reproduce most of the static and dynamic properties of the condensed phases of ethanol, while the need to take into account the real dipole moment of the isolated molecule by using a polarizable model is more evident in the low-density states. (C) 1999 American Institute of Physics. [S0021-9606(99)52016-3].