Pressure calculated with Poisson Boltzmann for counter ions between two charges surfaces.
See: A. Schlaich SUPPLEMENTAL MATERIAL for Simulations of nanoseparated charged surfaces reveal charge-induced water reorientation and non-additivity of hydration and mean-field electrostatic repulsion
https://pubs.acs.org/doi/suppl/10.1021/acs.langmuir.8b03474/suppl_file/la8b03474_si_001.pdf
