Implicit particle wall boundary condition in molecular dynamics

Thin film and nano-tube manufacturing, micro-channel cooling, and many other similar interesting techniques demand the prediction of heat transfer characteristics at the nanometre scale. In this respect, the transport properties at gas—solid and liquid—solid interfaces are very important. The processes at these interfaces can be studied in detail with molecular dynamics (MD) simulations. However, the computational cost involved in simulating the solid wall currently restrains the size of channels, which can be simulated. Therefore, the solid wall is sometimes replaced by boundary conditions, which often compromise on macroscopic quantities, such as density, temperature, pressure, and heat flux. In the current paper, a new particle wall boundary condition is presented, which is in good agreement with existing boundary conditions, but allows for the pressure calculation. This new boundary condition is based on averaging the contributions of an explicit solid wall and is derived using knowledge on common practices in MD algorithms, such as truncation and shifting. Moreover, it allows for different crystal lattices to be included in the new potential. The applicability of the new method is demonstrated by MD simulations of a gas between two parallel plates at different temperatures and densities. Furthermore, these simulations are compared with explicit wall simulations and existing boundary conditions.