[gmx-developers] introduce effective potential

[Nguyen Hoang Phuong]

Dear All,

I would like to replace the non-bonded potential energy functions
(Coulomb and vdW) by the effective potential

U_eff = KT*q/(q-1)*log(1 + (q-1)*[U + epsilon]/KT)

where q and epsilon are the parameters, U is the original
nonbonded potential.

This is equivalent to introduce the scale factor:

q/(1 + (q-1)*[U + epsilon]/KT)

into the forces which acting on the atoms.

To this end, I have modified to code which is used to calculate non-bonded
interactions src/gmxlib/fnbf.c

Because this code was written in assembly and it is very difficult for me
to add the scale factor. I would be very happy if someone can give
the hints.

I appreciate for any suggestion.

Phuong