Potential force barrier

Overcome potential energy barriers and force a molecule into a lower energy conformation than the one you might obtain using geometry optimization alone. 

The major drawback for employing the Car-Parrinello approach in dynamics simulations is that since a variational wavefunction is required, the electronic energy should in principle be minimized before the forces on the atoms are calculated. This greatly increases the amount of computer time required at each step of the simulation. Furthermore, the energies calculated with the electronic structure methods currently used in this approach are not exceptionally accurate. For example, it is well established that potential energy barriers, which are of importance to chemical reactivity, often require sophisticated methods to be accurately determined. Nonetheless, the Tirst-principles calculation of the forces during the dynamics is an appealing idea, and will continue to be developed as computer resources expand. 

This situation applies with weak hydrogen bonds at one extreme and very strong hydrogen bonds at the other with H and D confined to the same potential well. However, when the potential energy barrier has fallen sufficiently to allow the proton to escape the confines of its parent well, but leaves the deuteron trapped, then different values of the isotopic ratio can be observed (Fig. 7). The effect of isotopic exchange is now much more than merely one of doubling the reduced mass of the vibrating bond. When the proton is above the barrier, the force constant of the A—H bond, k A.—H),... 

The rate of deposition of particles onto a surface, in the presence of London, double-layer, and gravitational forces, is calculated in terms of the energy of interaction between cell and surface by assuming that Brownian motion over a potential energy barrier is the rate-determining step of the... 

This result, with a highly negative raises the possibility that the cells might be carried over the potential energy barrier by their own inertia. Inertial forces, ignored in the analysis leading to equation (13), may be evaluated from ... 

In moving from one location to another, relative to neighboring particles, a particle must surmount a certain potential energy barrier that arises from forces resisting movement. This effect is a function of both particle size and shape and is most... 

---