[gmx-users] Charges for Coulomb potential

[Delmotte, Antoine]

Dear Gromacs users,

I would like to know which charges are used by Gromacs in the 
calculation of electrostatic interactions in the standard coulomb potential:

E_electrostatics = 138.935 * q1 * q2 / (epsilon_r  * r_12);

Are q1 and q2 the values tabulated in the file "aminoacids.rtp" of the 
force field used?

Could you also please redirect me towards the relevant literature for 
the calculation of epsilon_r in Gromacs?  (or does Gromacs uses a fixed 
epsilon_r?)

Thank you very much in advance,

Antoine