MEPCO contours

The above G(a) surface is a molecular electrostatic potential contour surface, MEPCO, for the contour value a. Note that in contrast to the case of electronic charge density contours, in a MEP analysis the function V(r), hence the threshold parameter a, can take both positive and negative values. 

A variety of molecular surfaces can be defined in terms of the molecular orbitals Ti(r) of a molecule. A contour surface of an MO 4 j(r) is defined in terms of the level sets F(a) and its boundary surface G(a), with respect to a threshold a of the function value Ti(r). Similar to the case of MEPCO s, these threshold values may take both positive and negative values. 

For the characterization of the shapes of molecular contour surfaces, such as MIDCO s and MEPCO s, one may subdivide the surface into domains fulfilling some local shape criteria. One can distinguish two types of criteria, relative, and absolute, leading to a relative shape domain or an absolute shape domain subdivision of the molecular contour surface. 

For example, the technique of interpenetrating contour surfaces (157] can be applied for a relative shape domain subdivision of a pair of MIDCO and MEPCO surfaces of a molecule. The MIDCO surface can be subdivided into domains using the contour value of the MEPCO as criterion. This procedure is equivalent to generating the interpenetration pattern on the MIDCO surface [157]. 

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