Structural investigations of liquid formamide by x-ray scattering, ab-initio calculations and molecular dynamics simulations

Abstract

A structural investigation of liquid formamide is performed at room temperature and atmospheric pressure by x-ray scattering, ab-initio RHFMP2 calculations and classical Molecular Dynamics (MD) simulations. The experimental data were analyzed to yield the structure factor SM (Q) and the pair correlation function gL(r) of this liquid. A second order perturbation theory based on the Moller–Plesset partition (MP2) using the 6-311G** basis was employed to optimize the minimum energy structures of the monomer and some possible clusters. Among a large variety of dimers, trimers and one tetramer, it has been shown that some of them describe the intermolecular arrangement in the liquid. Our investigation clearly shows the existence of clusters other than crystal ones. Molecular Dynamics results using three different force fields show that x-ray scattering data can be reproduced quite well by classical MD simulations. The ab-initio calculations show that the C⋯O interactions are weaker than the N⋯O ones. This result is supported by the analysis of the partial correlation functions that show the existence of the strong N⋯O hydrogen bond in liquid formamide and the absence of a significant number of C⋯O hydrogen bonds.