A Combined Car - Parrinello QM / MM Implementation For Ab Initio Molecular Dynamics Simulations of Extended Systems

We have applied the method to determine the free energy barrier of the chain termination in a Ni-diimine based ethylene polymerization catalyst, 1. In this simulation the Ni diimine core was treated at the Becke88Perdew86 DFT level while the large ortho substituted aryl rings were treated with a molecular mechanics force field (The atoms with the asterisk in structure 1 are the capping atoms). We have performed a 40000 time step (7 ps) simulation of the termination process at 300 K giving a free energy barrier of 15 kcal/mol which is in excellent agreement with the experimental termination barrier of 16 kcal/mol. Without the bulky aryl ligands, the analogous pure QM simulation provided a barrier of 9.7 kcal/mol. We will also present our work on the incorporation of solvent effects through explicit MM solvent molecules into our multiple time step combined Car-Parrinello and molecular mechanics method.