Types of Potential Energy Surfaces

The calculation of potential energy surfaces of interacting atoms is a complicated quantum-mechanical problem. It was solved for very simple systems only (see [132, 134, 241, 322, 413]). Consequently, along with the ab initio calculations there are may semiempirical methods based on theoretical correlations between readily measurable molecular parameters. Moreover, direct models of the potential surfaces are widely used [243]. 

These models aim at the simplification of the potential surface in order to facilitate dynamical studies on atomic motions over the surface. Of course, both semiempirical and model potential surfaces must be based on correct qualitative 

---

HyperChem provides three types of potential energy surface sampling algorithms. These are found in the HyperChem Compute menu Single Point, Geometry Optimization, and Molecular Dynamics. 

It follows that the model potential (29.11) can reproduce three types of potential energy surfaces relevant to double proton transfer, as illustrated in Fig. 29.3(a)-(c). For G < 1/2 ( weak coupling ) it leads to surface (a) that supports a stable intermediate. For 1 /2 < G < 1 ( intermediate coupling ) it leads to surface (b) without... 

Studies of kinetic energy release distributions have implications for the reverse reactions. Notice that on a Type II surface, the association reaction of ground state MB+ and C to form MA+ cannot occur. In contrast, on a Type I potential energy surface the reverse reaction can occur to give the adduct MA+. Unless another exothermic pathway is available to this species, the reaction will be nonproductive. However, it is possible in certain cases to determine that adduct formation did occur by observation of isotopic exchange processes or collisional stabilization at high pressures. 

Figure 6.2 Disposition of potential energy surfaces for the interaction between excited and ground state molcules of a fluorescence A and a quencher B. (See text for explanation of (a), (b), (c) and (d) types.)...

Theoretically, one usually tries to understand reactions of the type (12) in terms of potential energy surfaces for electronic states of the molecule A2C. Whereas for the process... 

We will not discuss the actual construction of potential energy surfaces. This monograph deals exclusively with the nuclear motion taking place on a PES and the relation of the various types of cross sections to particular features of the PES. The investigation of molecular dynamics is — in the context of classical mechanics — equivalent to rolling a billiard ball on a multi-dimensional surface. The way in which the forces i fc(Q) determine the route of the billiard ball is the central topic of this monograph. In the following we discuss briefly two illustrative examples which play key roles in the subsequent chapters. 

---