Transition-state optimization on free energy surface: Toward solution chemical reaction ergodography

Abstract

To obtain a transition state (TS) in solution chemical reaction, a new TS optimization method has been proposed on a multidimensional free energy surface (FES). Analogous to the method for the Born–Oppenheimer potential energy surface using ab initio molecular orbital calculation, the present method utilizes force and Hessian on the FES, which can be calculated by molecular dynamics method and the free energy perturbation theory. Furthermore, on the basis of the method, we have proposed the definition of the intrinsic reaction coordinate (IRC) on the FES. According to not only the estimation of the computational demand but also the comparison of the numerical accuracy, we conclude that our method should be more efficient than such other methods that utilize only the free energy. Finally, it is discussed that the TS optimization and the IRC on the FES should become very important tools to develop a new research field called the solution chemical reaction ergodography. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 95–103, 1998