| Methods for including quantum mechanical effects in molecular dynamics (MD) simulations are discussed in this thesis. The thesis focuses on the path integral centroid molecular dynamics (CMD) algorithm. This algorithm is first described and then used in simulations of low temperature para-hydrogen, and also in simulations of the excess proton in water clusters and in the bulk. The CMD method allows one to include the effects of nuclear quantization approximately while still maintaining a quasi-classical, trajectory based, description of the dynamics. The effects of quantization of the electronic degrees of freedom are also discussed. These effects are usually taken into account implicitly through parameterized potential functions. However, methods for including the quantum electronic degrees of freedom explicitly in a MD simulation are also discussed in this thesis. Most notably, the Car-Parrinello method, which combines density functional theory (DFT) with MD, is employed with the CMD algorithm. This yields a method which takes explicit account of the quantum electrons and nuclei. Thus, this work represents one feasible approach for considering the quantum nature of all the degrees of freedom of the system while still maintaining an MD framework. In the concluding remarks, future directions and possibilities for this type of approach are discussed. |
