Equation ( ) follows a variational principle with respect to the induced moments and a preconditioned conjugate gradient method is used to find the ∆Q m t , which gives the minimum energy. Induced interactions are modified using Thole's damping functions to avoid overpolarization. Note that other classical environment models differ mainly by the specific expressions used for Eq. ( ) and Eq. ( ). Now turning toward the QM/MM setup, one can write its total energy as the sum of QM, MM, and QM/MM coupling terms, cf. also Eq. ( ):