For common condensed phase problems described by a low‐dimensional system coupled to a harmonic bath, Feynman’s path integral formulation of time‐dependent quantum mechanics leads to expressions for the reduced density matrix of the system where the effects of the harmonic environment enter through an influence functional that is nonlocal in time. In a recent Letter [Chem. Phys. Lett. 221, 482 (1994)], we demonstrated that the range of the nonlocal interactions is finite even at zero temperature, such that the nonlocal kernel extends over only a few time steps if the path integral is expressed in terms of accurate quasiadiabatic propagators. This feature arises from disruption of phase coherence in macroscopic environments and leads to Markovian dynamics for an augmented reduced density tensor, permitting iterative time evolution schemes. In the present paper we analyze the structure and properties of the relevant tensor propagator. Specifically, we show that the tensor multiplication scheme rigorously conserves the trace of the reduced density matrix, and that in cases of short‐range nonlocality it leads to Redfield‐type equations which are correct to all orders in perturbation theory and which take into account memory effects. We also argue that a simple eigenvector analysis reveals (without actual iteration) the nature of the dynamics and of the equilibrium state, and directly yields quantum reaction or relaxation rates.
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15 March 1995
Research Article|
March 15 1995
Tensor propagator for iterative quantum time evolution of reduced density matrices. I. Theory
Nancy Makri;
Nancy Makri
School of Chemical Sciences, University of Illinois, 505 S. Mathews Avenue, Urbana, Illinois 61801
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Dmitrii E. Makarov
Dmitrii E. Makarov
School of Chemical Sciences, University of Illinois, 505 S. Mathews Avenue, Urbana, Illinois 61801
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J. Chem. Phys. 102, 4600–4610 (1995)
Article history
Received:
September 08 1994
Accepted:
December 01 1994
Citation
Nancy Makri, Dmitrii E. Makarov; Tensor propagator for iterative quantum time evolution of reduced density matrices. I. Theory. J. Chem. Phys. 15 March 1995; 102 (11): 4600–4610. https://doi.org/10.1063/1.469508
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