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 operato r are presented. Numerical results for a symmetric double well potential ar e 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 the ory. QTST however, is found to always bounds the numerically exact result f rom above. QTST can be further improved, using a variational theory or by u sing the mixed quantum classical version of the theory. (C) 2001 Elsevier S cience B.V. All rights reserved.