In plane wave based electronic structure calcns. the interactions between core and valence electrons are in general represented by effective core potentials. These pseudopotentials are usually constructed such that the shape of the at. valence orbitals outside a certain core radius is reproduced correctly with respect to an atomistic all-electron calcn. As a new method we propose to tune addnl. parameters in the pseudopotentials in order to reproduce mol. properties from arbitrarily accurate ref. calcns. We demonstrate the validity of our approach by including dispersion interactions into DFT via the optimization of addnl. added pseudopotential parameters. Without inreasing the computational cost our scheme allows to conduct first principle DFT based mol. dynamics of large mol. systems taking dispersion forces into account. [on SciFinder (R)]