**The Discrete Reaction Field method** The DRF approach uses a polarisable force field which is (apart from the short range repulsion) based on second-order perturbation theory (ensures the correct analytical form of model potentials). Force field parameters are obtained from quantum chemical calculations where possible.

Source:

The discrete reaction field approach for calculating solvent effects

Duijnen, P.Th.van, Swart M. and Jensen L.

In: Solvation effects on molecules and biomolecules, S. Canuto, Editor. Springer. p. 39-103

http://theochem.chem.rug.nl/publications/PDF/ft608.pdf