THE REACTIVE FLUX METHOD APPLIED TO COMPLEX ISOMERIZATION-REACTIONS -USING THE UNSTABLE NORMAL-MODE AS A REACTION COORDINATE

A basic problem when calculating reaction rates using the reactive flu x method is the introduction of a reaction coordinate. In this paper w e show that it is advantageous to define a reaction coordinate by mean s of the unstable normal mode of the saddle point of the potential ene rgy surface. This particular choice is made since it yields a high tra nsmission function. Moreover, the reaction coordinate is calculated vi a a rapidly converging algorithm, and its derivative, which is needed in constrained runs, is calculated analytically. Calculations on the t ransmission coefficient of the isomerization of n-butane are in good a greement with results published by others. Runs with an isomerizing ca lix[4]arene in vacuo produce a very high transmission coefficient, as is the purpose of the reaction coordinate. The same molecule is also s tudied in chloroform. (C) 1997 American Institute of Physics.