نرگس مهدی پور

It is known that pair potentials are not adequate to correctly describe the structure and dynamics of liquid metals. In this work many-body interactions in fluid sodium are taken into account through the generic form of the forces acting between fluid particles in the context of the many-body dissipative particle dynamics (DPD) simulation. It is shown that this method accurately takes into account the role of many-body interactions in the improvement of the equation of state and structural properties of sodium. A comparison of our calculated coexisting liquid and vapor densities with experiment indicates that this model well predicts the vapor pressure and the densities over a broad range of temperatures. Also the calculated radial distribution functions are in very close agreement with experimental values. However, the calculated diffusion coefficient of sodium at low temperature deviates considerably from experiment. Although the soft-core “pair” potential in the original DPD method results in an equation of state exhibiting no fluid?fluid phase transition, the present “many-body” DPD approach successfully predicts the liquid?vapor coexistence curve of sodium. This occurs because, in the many-body DPD model, the force acting on a pair of atoms depends not only on their positions but also on the positions of all their other neighboring atoms. Also calculations are done using “pair” potentials and using the potential of mean force (in which the effect of many-body interactions are implicitly taken into account). It is shown that the results obtained using the many-body DPD approach are more accurate than those obtained employing both pair potentials and potential of mean force.