Flexible Molecular Model of Methanol for a Molecular Dynamics Study of Liquid and Supercritical Conditions

A new flexible molecular model of methanol was developed for computer simulations applicable to conditions from the liquid to the supercritical state. The proposed model considered methanol as three interaction sites, oxygen atom, methyl group, and hydrogen atom, and was represented as the sum of intramolecular and intermolecular potentials. The intramolecular potential function introduced a Toukan−Rahman potential and the intermolecular potential function applied an OPLS function. The potential parameters were adjusted to represent the experimental saturated liquid density of methanol at 25 °C. The estimated critical point of the proposed model (T C = 232.2 °C, ρC = 0.278 g·cm-3) was found to be close to the experimental critical point. Transport properties and vibrational spectra were in good agreement with the literature values. The fluid structure of methanol was studied via analyses made on the spatial distribution function. Methanol was found to have chainlike structures in the liquid state and perturbed structure at supercritical conditions. From the analyses, roughly half of the hydrogen bonding molecules in the liquid state were preserved even in supercritical conditions.