Pressure-Consistent Iterative Boltzmann Inversion for Coarse-Grained Molecular Dynamics

Bottom-up coarse-graining enables efficient simulation of complex molecular systems at mesoscopic scales. Many methods capture structural features well but often overestimate pressure, as computed by the virial theorem, due to thermodynamic representability issues. This limits utility, particularly for studying phenomena using the isothermal-isobaric (NPT) ensemble. Here, we present and analyze straightforward extensions of iterative Boltzmann inversion (IBI) that include pressure corrections during parameter optimization. Two new approaches are explored: iterative length scale rescaling (iLS) and iterative linear correction (iLC). These approaches differ from the more common practice of adding long-range attractive forces only after CG potential optimization. Performance is evaluated across diverse molecular systems, including polymer melts and molecular liquids, at varying CG resolutions. Both methods retain structural fidelity while enhancing thermodynamic consistency through reasonable modifications of the pair potential. In particular, resulting CG models accurately reproduce radial distribution functions, densities, and density fluctuations, with iLS exhibiting improved stability and faster convergence. Analysis of isothermal compressibility reveals a general resolution-dependent trend, with significant deviation from atomistic behavior emerging below a critical CG resolution. These findings demonstrate that iLS and iLC are practical, transferable methods for constructing coarse-grained models with consistent thermodynamic behavior. They also provide insights into limits of fidelity based on the resolution of CG models.