Intramolecular potential, quadratic

The linear form of the dynamic equation is consistent with the Gaussian distribution adopted throughout this chapter, which in turn produces a quadratic intramolecular potential of the form given in Eqn. (2.1.43) for the state. However, in the more general case of a polymer chain not in the 0 state. 

The spring constants are weaker and clear intramolecular distributions develop. The bond angles are controlled by potentials quadratic in the bond angle, with an equilibrium value of 0Q = 113,3 and k = 1,3 x 10 J mole . The simulation of these models is particularly simple. Atoms are treated independently and Newton s equations are solved using a leap-frog algorithm with a short time step, (At (H2O) = 2,5 x 10" s... 

Rahman potential is an extension of the SPC model. The extension is the inclusion of quadratic stretch and bend terms, so that internal degrees of freedom are present. The model was used to examine the effect of the liquid environment on internal modes, and the pair functions were found to be close to those for the SPC model. In contrast. Teleman et al., ° who used the same SPC model with a harmonic intramolecular potential, reported some large effects on properties. However, Barrat and McDonald find that flexibility has a small effect on calculated properties, stating... 

The intramolecular potential, E, can therefore be seen to have the usual quadratic form... 

Another way to approach the problem of the intramolecular potential in polyconjugated systems is to carry out quantum-mechanical calculations that provide quadratic force constants to be used in classical dynamical calculations as in Eq. (4). Also in this field arbitrary decisions must be made, thus undermining the importance and the faith in ab initio calculations. There are two types of approximations generally involved in ab initio calculations ... 

It factorizes into an intermolecular (the first term) and an intramolecular (the second term) factor. As predicted in Section 7.2 in general terms, the dissociation rate depends quadratically on the coupling potential Vi(R). 

---