A scheme is proposed for calcg. electrostatic potential (ESP) derived charges from mixed quantum mechanics/ mol. mechanics (QM/MM) mol. dynamics simulations. These charges are fitted to the electrostatic field due to the quantum charge d. evaluated on the MM atoms close to the QM system and are restrained to the corresponding Hirshfeld value by a quadratic penalty function. The D-RESP charges estd. by this procedure reproduce the field due to the charge d. polarized by the environment and can be obtained as a function of time along a finite temp. mol. dynamics trajectory with essentially no computational overhead with respect to a std. QM/MM calcn. The fluctuation of the D-RESP values in a finite temp. run provide information about the importance of polarization effects and thus allow for a direct comparison of the relative performance of polarizable vs. non polarizable point charge models. Moreover, the D-RESP charges estd. by this procedure can be used as a simple and straightforward indicator of the chem. state of the system. [on SciFinder (R)]