APPLICATIONS OF QUANTUM-CLASSICAL AND QUANTUM STOCHASTIC MOLECULAR-DYNAMICS SIMULATIONS FOR PROTON-TRANSFER PROCESSES

Quantum-classical and quantum-stochastic molecular dynamics models (QC MD/QSMD) are formulated and applied to describe proton transfer proces ses in three model systems - the proton bound ammonia-ammonia dimer in an external electrostatic field; malonaldehyde, which undergoes a qua ntum tautomeric rearrangement; and phospholipase A2, an enzyme which i nduces a water dissociation process in its active site followed by pro ton hopping to a histidine imidazole ring. The proton dynamics are des cribed by the time-dependent Schrodinger equation. The dynamics of the classical atoms are described using classical molecular dynamics. Cou pling between the quantum proton (s) and the classical atoms is accomp lished via conventional or extended Hellmann-Feynman forces, as well a s the time-dependence of the potential energy function in the Schrodin ger equation. The interaction of the system with its environment is de scribed by stochastic forces. Possible extensions of the models as wel l as future applications in molecular structure and dynamics analysis will be briefly discussed.