In spite of persistent effort for several decades, fully quantum mechanical simulation of the dynamics of systems with many degrees of freedom remains impractical.  Treating the solvent particles via classical trajectories, while retaining a fully quantum mechanical description for select degrees of freedom, is a very attractive option.  However, interaction of a delocalized wavefunction with classical trajectories is possible only via mean-field approximations. <br/>We have developed a rigorous quantum-classical path integral (QCPI) methodology which does not suffer from these issues because the quantum paths are local in space.  However, the number of system paths, as well as the number of classical trajectories to be obtained, grows exponentially with the number of propagation steps.  We are able to overcome the resulting computational problems by exploiting the nature of decoherence, which includes classical and quantum mechanical components.  Pretreating the classical decoherence, which is dominant at high temperatures, provides an excellent starting point, and the residual quantum decoherence is fully accounted for via phase interference among quantum paths.  Applications show that rigorous QCPI calculations on complex systems are feasible.  <br/>

Quantum-classical path integral: A rigorous methodology

249th National Meeting (2015)

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