Angle-bending potential

In a Urey-Bradley force field, angle bending is achieved using 1,3 non-bonded interaction rather than an explicit angle-bending potential. The stretch-bond term in such a forci field would be modelled by a harmonic function of the distance between the 1,3 atoms ... 

Fig. 10. Sketch of angle-bending potential of the form E = k2(0 - 0)2 + 4( - 0)4 with k2 = -70 kcal mol1 radian-2 and k4 = 93 kcal mol1 radian 1.

A molecule-independent, generalized force field for predictive calculations can be obtained by the inclusion of additional terms such as van der Waals and torsional angle interactions. This adds an additional anharmonic part to the potential (see below) but, more importantly, also leads to changes in the whole force field thus the force constants used in molecular mechanics force fields are not directly related to parameters obtained and used in spectroscopy. It is easy to understand this dissimilarity since in spectroscopy the bonding and angle bending potentials describe relatively small vibrations around an equilibrium geometry that, at least... 

Figure 8 MM3 and UFF bond angle bend potential energy functions = 39 kcal-mol ...

It is worthy of note that in MD studies of zeolites, the use of Eq. [17] for the T-O-T angle-bend potential conceals a pitfall as a result of the high degree of flexibility of these angles. Indeed, defining the T1-O-T2 angle 0 via 0 = arccos (cos 0) where... 

On the Representation of Angle Bending Potentials in Empirical Force Fields. ... 

The results underline on one hand the importance of a proper high-level theoretical treatment of such systems, which are difficult to describe because of the shallow-angle bending potential, and on the other hand they also underline the importance of experimental structure determinations in the gas phase (Table 2). 

The functional form of the angle bending potential in this force field (Maple et al., 1994) is ... 

Most of the flexible water potentials employ stiff (harmonic) bond-stretching and angle-bending potentials and do not allow for bond forming and breaking. The solvation of single structures, either H30 or OH, in the aqueous solution and at interfaces has been modeled with reasonable success using... 

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