Interface to libefp provides means to perform simple QM/MM calculations and constrained QM region geometry optimziations. In this case, the fragment potentials should include MM_CHARGE and MM_LJ sections, see https://libefp2.github.io/parameters.html#additional-efp-parameters for detail. Keyword EFP_QMMM specifies the type of interactions between the QM and MM regions and between the MM (EFP) fragments, with options being mechanical and electrostatic embedding and a mixed model, in which the polarizable QM/EFP calculation is augmented by Lennard-Jones interactions between the QM and EFP regions.
Geometry optimziation of the QM region is enabled for the electrostatic embedding scheme (EFP_QMMM = 2). The MM region remains rigid; only the QM atoms are subjected to optimization in cartesian coordinates.