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The
two diagrams of potential as a function of position illustrate the concept
of a saddle point. In the top picture a one-dimensional situation is considered.
In moving from the local minimum (a) to the local minimum (c) the system
has to pass through the metastable location (b) with free energy, Gb.
This position is the saddle point for the jump (a) -> (b).
The
two-dimensional case is illustrated below and is a true saddle point. It
is a local maximum as far as the jump between the two blue potential wells
is concerned, but also a local minimum with respect to transverse displacement
of the red path. In this case the potential used as an example is associated
with the hydrogen configurations of a triatomic HCN molecule. |
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