The effect of intermolecular potential model on the structure and conformational equilibrium of liquid n-butane

Several Monte Carlo simulations with a sample of 125 molecules of n-butane with four Lennard-Jones centers and internal rotation, have been carried out by varying the values of ε and σ parameters of the intermolecular potential. In this way the effect of such changes on the thermodynamic, structural, and conformational properties have been studied. Although the structure remains practically unaffected by moderate variations in the Lennard-Jones parameters, nevertheless the conformational equilibrium is very sensitive to them. Also specific properties of chain molecules in the n-butane, such as the effect of the relative position of centers (external vs internal ones) and the possibility of orientational correlation have been explored. The difference between the effects of the external centers vs the internal ones can be quantified and it turns out to be significant; on the other hand the orientational correlation is very weak at room temperature and normal liquid density.