Electrostatic potential maps
The same Spartan02 computer program that is used to
construct molecular models, and calculate model electron density
clouds, is also be used to calculate model electrostatic potentials.
The process is complicated because the program must calculate the
interaction between the +1 probe charge and every part of the electron
density cloud, and it is necessary to divide the cloud into many
small pieces to do this accurately.
The display of electrostatic potential data is another
difficult problem. We cannot look at the potential everywhere simultaneously,
so we must select some points of interest first, and display the
potential at these points.
Spartan02 selects the points located on the molecule’s
size density surface (0.002 au isodensity surface) and calculates
the potential at these points. Then Spartan02 assigns colors to
these points according to their potential (the rules for selecting
colors is explained in the next section). The resulting rainbow-colored
surface is called a potential map. The two-step scheme leading
from molecule to size density surface to colored potential map is