# [gmx-users] Interaction energy with Reaction-field

Caceres Delpiano J. j.caceresdelpiano at soton.ac.uk
Tue Aug 28 17:02:09 CEST 2018

Hello everyone,

this is my first time asking something in here, so I'm going to try to be as clear as possible.

Im trying to calculate the electrostatic interaction energy of an ion with the surrounding solvent (water) using a reaction-field scheme. Im interested to know the interaction energy within R_c (cutoff) betweens these two groups, but Im confused with the definitions when I run gmx energy. Which term should I be looking for? RF-excl, Coul-SR:ION-SOL? both of them? What I bassically want to know is the average value of equation 4.13 in the manual, for all pairs within R_c, for these two groups

V_crf = f*q_i*q_j*[\frac{1}{r_ij} + k_rf*r^2_ij - c_rf]

I'm using a charged group scheme for this, and I have assigned the charged group numbers explicitly in the topology.

Thank you for your time and help.

Best,
Javier.