Potential energy characteristics for chemical reactions

Ab initio molecular orbital (MO) methods are used to provide accurate descriptions of potential energy surfaces for chemical reactions. Thus, far, this has been limited with respect to systems having four or more atoms. However, computer calculation of the energy gradiant with respect to nuclear coordinates is now coming into use. In this review, the analytical calculation of the energy gradient is summarized. The methods of determining geometries, force constants, and normal vibrations for both equilibrium configurations and saddle points are discussed. The intrinsic reaction coordinate is also calculated. Examples of calculations are given