Recent progress in simulation methodology and computer power has made free energy calculations of chemical and biological processes in the condensed phase based on ab initio potentials largely accessible.In this talk,I will report our work on computational enzymology using ab initio QM/MM molecular dynamics simulation combined with polarizable force field to elucidate both the reaction mechanism in the active site of enzymes and the orgin of their catalytic power.The interesting enzymatic systems we will discuss include the ribozyme ribosome and the protein enzyme DNA polymerase.Multidimensional free energy surfaces obtained directly from density functional theory calculations will be presented.Most importantly,our study has led to the finding that proteins electronic polarization contributes significantly to their catalytic functions.