Comparison of positive flux operators for transition state theory using a solvable model

Several quantum operators representing ‘‘positive flux’’ are compared for the square barrier by examining their ability to reproduce the exact transmittance when traced with the exact microcanonical density operator. They are obtained by means of the ‘‘Weyl rule,’’ the ‘‘Rivier rule,’’ by symmetrizing the product of ‘‘flux’’ and ‘‘positive momentum projection’’ operators, and by a variational technique. Explicit expressions are given for all cases.