Short range order of methanol

Abstract

The structure of liquid methanol has previously been investigated using experimental and computational methods, such as density functional theory and molecular dynamics simulations. Some studies suggested that the liquid consists of cyclic structures and others of open chains of molecules, without agreement. We apply the quasi-crystalline model to analyze the short-range order represented in the radial distribution functions obtained from neutron diffraction experiments. This analysis is complemented by molecular dynamics simulations of methanol with the OPLS/2016 potential to obtain the radial distribution functions. The reference short-range orders examined in the model were selected from observed and proposed solid phases of methanol. The short-range order at T=-80°C and at ambient conditions matched that of the α-phase, corresponding to open chains, and the short-range order at T=253°C and P = 14.3 MPa matched the 4R structure corresponding to cyclic tetramer. We found no suitable structure to represent the order for the sub-critical and super-critical states, T = 253 °C and P = 117.7 MPa and T = 202 °C and P = 73.7 MPa. The OPLS/2016 radial distribution functions from the molecular dynamics simulations did not fit the experimental site-site radial distribution functions. However, the short-range orders found at ambient conditions and T=-80°C for the computed radial distribution functions with the quasi-crystalline model, agree with those found on the experimental radial distribution functions.