Algorithm to enforce uniform density in liquid atomistic subdomains with specular boundaries

An important component in hybrid atomistic-continuum (HAC) modeling of liquids is the proper termination of the atomistic subdomain (ΩA). When the HAC model is based on the Schwarz domain decomposition method, the total number of particles in ΩA is conserved using specular boundaries in an overlap region, where information is exchanged with the continuum subdomain (ΩC). This non-periodic termination of ΩA fails to account for forces otherwise included in a periodic system, through the minimum image convention. The absence of such forces results in spurious density fluctuations adjacent to the specular boundaries. In this work, we present a new boundary force algorithm that establishes a uniform density profile at non-periodic boundaries of ΩA. We also examine the effects of the non-periodic termination of ΩA on the liquid properties. The algorithm relies on force measurements carried out over a spatially discretized atomistic subdomain. It is relatively straightforward to implement and can be seamlessly extended to higher dimensions.