Qmmm eref

From NWChem

eref <double precision default 0.0d0>

This directive sets the relative zero of energy for the QM component of the system. The need for this directive arises from different definitions of zero energy for QM and MM methods. In QM methods the zero of energy for the system is typically vacuum. The zero of energy for the MM system is by definition of most parameterized force fields the separated atom energy. Therefore in many cases the energetics of the QM system will likely overshadow the MM component of the system. This imbalance can be corrected by suitably chosen value of eref. In most cases IT IS OK to leave eref at its default value of zero.