Hi,

I run a simulation in which 2 molecules charged by gaisteger method using dreiding forcefield were solvated with water which was manually charged with SPC model charges. The summation method was set to Ewald for electrostatic terms and group summation for VDW. During analysis, I used the forcite module to calculate energy using the same summation method as the simulation.

A warning read, 'An Ewald summation has been chosen for the electrostatic terms. The current
implementation assumes that all interactions are of the form F(1/Rij), but the forcefield contains other terms. They will all be treated as F(1/Rij). Warning: The system has a net charge of 1.20002 e. The chosen summation method will add a uniform background charge of -1.20002 e to neutralize.'

I also repeated the energy calculation using group based summation for both electrostatic terms and VDW and the error did not come up. I have attached photos of the energy differences.

Am I to disregard the energy results with ewald's summation? is the warning about the charges something of concern? Is it acceptable to calculate the energy using a different summation method from the one used in the simulation?