APBS and PDB2PQR: electrostatic and solvation properties for complex molecules.

APBS solves the equations of continuum electrostatics for large biomolecular
assemblages. This software was designed "from the ground up" using modern design
principles to ensure its ability to interface with other computational packages
and evolve as methods and applications change over time.

WWW: https://www.poissonboltzmann.org/