A molecular dynamics study on the role of attractive and repulsive forces in isobaric heat capacity and sound velocity of sub- and supercritical dense fluids

•We investigate the role of attractive and repulsive forces on isobaric heat capacity and sound velocity in dense fluids and liquids.•The sound velocities resulting from repulsive intermolecular interactions are greater than those of LJ potential.•The repulsive forces play the main role in causing the isobaric heat capacities at high temperatures and pressures.•The sound velocities resulting from attractive intermolecular interactions are negative. In this study, the role of attractive and repulsive forces on isobaric heat capacity and sound velocity in dense fluids and liquids has been investigated using a molecular dynamics simulation technique. Lennard-Jones potential is divided into attractive and repulsive parts. From the molecular dynamics calculations, enthalpies and isobaric heat capacities have been obtained for Argon at temperatures of 120–800K and constant pressures of 100–800MPa. The sound velocities have been calculated at 250 and 400K. The repulsive forces play the main role in causing the isobaric heat capacities at high temperatures and pressures. With decreasing temperature at constant pressure, the role of attractive forces considerably increases. The sound velocities resulting from attractive intermolecular interactions are negative which is physically unrealistic. This indicates the essential role of repulsive forces in the determination of sound velocities.