Area-weighted surface charge of hydrogen bonding acceptor atoms HACA2

Definition:

^S_A - solvent-accessible surface area of H-bonding acceptor atoms, selected by threshold charge

q_A - partial charge on H-bonding acceptor atoms, selected by threshold charge

S_tot - total solvent-accessible molecular surface area 

Reference:

1. D.T. Stanton, P.C. Jurs, Anal. Chem., 1990, 62, 2323; D.T. Stanton, L.M. Egolf, P.C. Jurs, M.G. Hicks, J. Chem. Inf. Comput. Sci., 1992, 32, 306.