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Center for Nonlinear Studies |
A recently introduced computational approach for simultaneous quantum wavepacket and ab initio molecular dynamics of electrons and nuclei is discussed. The approach is based on a synergy between quantum wavepacket dynamics and ab initio molecular dynamics. The quantum dynamics is performed using an efficient banded, sparse and Toeplitz representation for the discretized free propagator that is formally exact. Ab initio molecular dynamics is achieved by using (a) an extended Lagrangian formalism, known as atom-centered density matrix propagation, (b) Born-Oppenheimer dynamics. A fundamental difficulty in this approach is that the interaction potential between classical and quantum part of the system needs to be computed at every dynamics step. We overcome this problem dynamically using a "time-dependent deterministic sampling" (TDDS) procedure combined with potential interpolation. This procedure greatly reduces computational cost of the method by orders of magnitude. The example calculations dealing with hydrogen transfer in small ionic clusters and Soybean Lipoxygenase (SLO-1) catalyzed oxidation of fatty acid are discussed. The nature of kinetic isotope effect (KIE) in SLO-1 reaction is dominated by quantum tunneling an vibrational excited states of hydrogen.