Extending pressure-matching to inhomogeneous systems via local-density potentials

Bottom-up coarse-grained models describe the intermolecular structure of all-atom (AA) models with desirable accuracy and efficiency. Unfortunately, structure-based models for liquids tend to dramatically overestimate the thermodynamic pressure and, consequently, tend to vaporize under ambient conditions. By employing a volume potential to introduce additional cohesion, self-consistent pressure-matching provides a simple and robust method for accurately reproducing the pressure equation of state (EoS) for homogeneous fluids, while still preserving an accurate description of intermolecular structure. Because they depend upon the global density, though, volume potentials cannot be directly employed for inhomogeneous systems, such as liquid-vapor interfaces. In the present work, we demonstrate that volume potentials can be readily adapted as potentials of the local density. The resulting local-density potentials provide an accurate description of the structure, pressure EoS, and local density fluctuations of an AA model for liquid methanol. Moreover, we demonstrate that very slight modifications to these local-density potentials allow for a quantitative description of either local or global density fluctuations. Most importantly, we demonstrate that the resulting potentials, which were parameterized to describe a homogeneous liquid, also generate stable liquid-vapor coexistence. However, further work is necessary to more accurately reproduce the interfacial density profile.