Structure based coarse-grained models typically overestimate the system’s pressure. We previously resolved this issue by employing a global density dependent term in the approximation to the potential of mean force that we parameterized via iterative pressure matching. We then demonstrated that changing this potential into a function of the local density around each particle provides a reasonable estimate of the equation of state which can be improved through slight adjustments to the local density potential. We have now parameterized local density potentials via the multi-scale coarse-graining method from atomistic simulations of liquid-vapor interfaces. We compare and contrast the advantages and drawbacks of the two different parameterization schemes. Additionally, we use the generalized Yvon-Born-Green framework to analyze the sources of structural features that frequently arise during coarse-grained simulations employing local density potentials that are absent from the atomistic simulation. We show that an imbalance of attractive and repulsive forces arising from the local density and pair potentials causes various levels of bunching at the interface. Furthermore, we implemented external basis functions in our force matching code to help our models reproduce the density distribution as well as the average mapped atomistic force, with the option to include the corresponding external potential. Finally, we demonstrate that the basis vectors for the standard pair potential and the local density potential are non-orthogonal, which results from the decomposition of the local density force into a sum of pairwise contributions. As a result, given an initial pair potential and local density potential, it is possible to construct an infinite number of other sets of pair potentials and local density potentials that produce the exact same forces, by making one more attractive and the other one correspondingly more repulsive.

Bottom-up coarse graining of inhomogeneous environments

2019 Fall National Meeting

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