RELIABILITY OF THE SINGLE-POINT CALCULATION TECHNIQUE AT CHARACTERISTIC POINTS OF THE POTENTIAL-ENERGY SURFACE

The errors associated with the application of the single-point calculation technique in the construction of the reaction path were analyzed in terms of both energy and entropy. Since the lower and higher levels yield curves that are shifted relative to each other, this technique has a destabilizing effect at the minimum (E' error), while, at the saddle point, it has a stabilizing effect on the reaction coordinate (E '' error) and a destabilizing effect on the remaining coordinates (E'(SP) error). Likewise, along the minimum energy path, this technique artificially locates the maximum away from the saddle point. To regard this shift away from the saddle point as a variational effect would be a conceptual error. A modification of the technique is proposed that avoids these computational and conceptual errors.