Quantum transition state theory for dissipative systems

Two formulations of quantum transition state theory (QTST) for dissipative systems, based on the symmetrized and Kubo form of the thermal flux operator are presented. Numerical results for a symmetric double well potential are compared with the numerically exact results of Topaler and Makri [J. Chem. Phys. 101 (1994) 7500] and with centroid transition state theory. The two forms give similar answers and are similar in accuracy to the centroid theory. QTST however, is found to always bounds the numerically exact result from above. QTST can be further improved, using a variational theory or by using the mixed quantum classical version of the theory. (C) 2001 Elsevier Science B.V. All rights reserved.