The PM7 method is to be used. This keyword is redundant, because the default method in MOPAC2016 is PM7. See also PM7 Accuracy

Notes on PM7

PM7 uses a "D2" type correction.  Elements supported are:  H, He, B, C, N, O, F, Ne, P, S, Cl, Ar, Br, and Kr.  For the other elements, a core-core Gaussian attractive terms is used to mimic dispersion.  This means that some form of dispersion is present for all elements.  The core-core Gaussian terms are optimized to reproduce reference geometries and heats of formation.