Greetings Neha,
These are the sorts of =
calculations my group spends a lot of time on. To computer the electr=
ic field at a point we insert dummy atoms with zero charge around the point=
of interest and, using the "write atompot flat" keyword, apbs calculates t=
he potential at each atom. We then take the negative potential gradie=
nt along each vector we have dummy atoms. ie:
^ yWhere DZN is dummy atom N along vector Z. The Ey =3D - (p=
otential_Dy2 - potential_Dy1)/(position_Dy2 - position_Dy1) and Ex =3D=
- (potential_Dx2 - potential_Dx1)(position_Dx2 - position_Dx1). Clea=
rly this is trivially expanded into 3 dimensions.