Surface Tension Evaluation of Lennard-Jones Fluid System With Untruncated Potentials

In typical atomistic simulations of simple liquids, the Lennard-Jones interatomic pair potential is truncated so that algorithms scale as Natoms rather Natoms2, which would be the case if an interaction were computed explicitly for all atom pairs. However, it is known that interfacial properties are sensitive to the cutoff radius selected. Corrections for the missing ‘tails’ of the potential can reduce the error, but cannot eliminate it because the liquid and vapor densities are also sensitive to the cutoff radius. In light of this, we have developed and implemented a NlogN particle-particle particle-mesh (P3M) algorithm to evaluate the 1/r6 dispersive forces between Lennard-Jones fluid molecules without truncation. Statistical expression for the surface tension also scale as N2 if potentials are not truncated, so we also developed a P3M formulation for computing surface tension. The techniques are demonstrated on a thin liquid film suspended in equilibrium with its own vapor. Simulations at several temperatures between the triple point and the critical point are compared with the available data. The expense of the algorithm is competitive for simple geometries and seems preferable in non-trivial geometries without the possibility of tail corrections.