Both terms forms the so-called non-bonded interaction energies and forces.

The vdW term consists of an attractive and a repulsive term (also denoted Lennard-Jones 6-12 interactions) and for two atoms ( i and j ) separated by a distance rij (in Å) and intervened by 3 explicit bonds or more, the additive pair-potential is given by

rm = 0.5*(rim+rjm)

eps = sqrt(epsi*epsj)

EvdW=4*eps[(rm^12)/rij^12) - (rm^6/rij^6)]

and the electrostatic part is Coulombic in nature, thus

Eelec = 332qi*qj/rij

where qi and qj are the charges (in protonunits) on each atom.

and E=Eelec+Evdw

Note that other polyexponentials can be used for the LJ pair-potential, and that rim=sigma^(-5/6) , where sigma is the conventionally termed vdW radii for atom i.