During this fiscal year we devoted major effort to work aimed at introducing polarizability into molecular force fields. Much of the work involved examining multipole expansions as a way to build accuracy into force field calculations. In one of the published studies it was shown that both static and geometry-dependent multipole models are able to reproduce total molecular forces and torques with repect to ab initio, whereas geometry-dependent multipoles are necessary to reproduce ab initio atomic forces. In another published work, a finite field method for calculating spherical tensor molecular polarizability tensors by numerical derivatives of induced molecular multipole with respect to gradients of the electrostatic potential are developed for arbitrary l and l'. These developments should be useful for the development of newer force fields that can be used to more accurately describe bio-macromolecules. Finally, we have developed code for partitioning the electron density into atomic contributions within the Hirshfeld-Iterated scheme. The codes developed in these studies are freely available.
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