Statistical mechanics of quantum-classical systems

The statistical mechanics of systems whose evolution is governed by mixed q uantum-classical dynamics is investigated. The algebraic properties of the quantum-classical time evolution of operators and of the density matrix are examined and compared to those of full quantum mechanics. The equilibrium density matrix that appears in this formulation is stationary under the dyn amics and a method for its calculation is presented. The response of a quan tum-classical system to an external force which is applied from the distant past when the system is in equilibrium is determined. The structure of the resulting equilibrium time correlation function is examined and the quantu m-classical limits of equivalent quantum time correlation functions are der ived. The results provide a framework for the computation of equilibrium ti me correlation functions for mixed quantum-classical systems. (C) 2001 Amer ican Institute of Physics.