RM1

The RM1 method(1) is to be used.

(1) Rocha, G.B., R.O. Freire, A.M. Simas, and J.J.P. Stewart., RM1: A Reparameterization of AM1 for H, C, N, O, P, S, F, Cl, Br, and I. J. Comp. Chem., 27(10): 1101-1111 (2006).