Anharmonicity potential energy surface

Fig. 1.3. Upper Schematic view (dotted line) of cross-section of many-dimensional highly anharmonic potential energy surfaces for reactants plus solution (R) and (dotted line omitted) for products plus solution (P). TS occurs at the intersection. Lower Plot of free energy G for the above R and P systems vs. the reaction coordinate U.

The anharmonic free energy is evaluated for empty hydrate and cubic ice (ice Ic). The calculated free energy due to the anharmonic potential energy surface is given in Table 1. The anharmonic contribution to the free energy of empty... 

The Ar-HF molecule serves as both a prototype for inert gas atoms clustering or solvating around a hydrogen-halide polar center and as a simple test-bed for refining and testing how we create anharmonic potential energy surfaces. Specifically, both the Ar-HF and the Ar-Ar potential energy surfaces are extremely well characterized and have been verified extensively... 

Venuti E, Halonen L, Delia VaUe RG (1999) High dimensional anharmonic potential energy surfaces The case of methane. J Chem Phys 110 7339... 

In conclusion, the work presented here has illustrated the effect of various potential energy surface properties on unimolecular dynamics. The calculations show that the energy distributions of the unimolecular products contain very little information about the intramolecular dynamics of the species undergoing unimolecular dissociation. It was also found that anharmonic potential energy surfaces may contain large fractions of quasiperiodic trajectories above the unimolecular threshold. 

Hobza, P., Bludsky, O. Suhai, S., 1999, Reliable Theoretical Treatment of Molecular Clusters Counterpoise-Corrected Potential Energy Surface and Anharmonic Vibrational Frequencies of the Water Dimer , Phys. Chem. Chem. Phys., 1, 3073. 

Even when the harmonic approximation is not quantitatively justified it provides a convenient starting point for exact treatments. Thus, even if the potential energy surface is anharmonic in the bottleneck, it is often smooth enough for there to be a principal saddle point that can be found by minimizing IVU 2. 

Such a method has recently been developed by Miller. et. al. (28). It uses short lengths of classical trajectory, calculated on an upside-down potential energy surface, to obtain a nonlocal correction to the classical (canonical) equilibrium probability density Peq(p, ) at each point then uses this corrected density to evaluate the rate constant via eq. 4. The method appears to handle the anharmonic tunneling in the reactions H+HH and D+HH fairly well (28), and can... 

---