The other default surface has a value of 0.002 and shows the outer edge of the molecule. This surface is used to study the interaction of a molecule with other molecules. In other words, the surface is used to study the intramolecular forces and the density surface the intermolecular forces. Together these surfaces show the chemical bonds in a molecule. These surfaces are the same as the electron density isosurfaces, but the property used is electrostatic potential.
Electrostatic potential is the force felt by a charge placed around a molecule.
The charge will be attracted or repel by a force of a certain strength. Therefore, electrostatic potential has both a magnitude and positive or negative sign. Where the electrostatic potential is negative, there is a surplus of electrons and this part of the molecule has a negative charge. Likewise, where the electrostatic potential is positive, there is a deficit of electrons and this part of the molecule has a positive charge. Electrostatic Potential Plots Superimposing electrostatic potential plots on the 0.002 isosurface makes intermolecular forces easier to visualize and predict.