By default, the set of approximations and the parameter set used in starting a parameterization is PM8. This can be changed by explicitly setting the method by the appropriate keyword. Allowed methods are:
MNDO, AM1, PM3, RM1, MNDOD, PM6, PM6-DH+, PM6-DH2, PM6-D3H4, PM6-DH2X, PM6-D3H4X, PM6-D3, PM6-D4(H4), PM7, PM7-HH, PM7-, and PM8
Most of these methods should only be used for surveys, serious development should be limited to PM6-D3H4X and PM8.