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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 shown below.
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