Materials Studio provides the option of generating the electron density difference in two different ways:
The former option produces a density difference field which shows the changes in the electron distribution that are due to formation of all the bonds in the system. This object is appropriate for bulk solids to illustrate the charge redistribution due to chemical bonding.
The latter option generates a density difference field which effectively corresponds only to the formation of bonds between atoms in different sets and to charge redistribution within the sets that is due to the presence of other sets. This property is useful to describe such processes as bonding of molecule(s) to external and internal (for example zeolites) surfaces, or creation of large molecules from smaller fragments.
Materials Studio supports the calculation of the density difference with respect to the densities of sets of atoms only for tasks that do not involve changes in atomic geometry. For Geometry Optimization and Dynamics values of the Task property, you can request this type of density difference after the run is complete by using the Properties task.
To perform an electron density difference analysis
Multiple sets should be mutually exclusive.
When only one set with the correct name is present in the structure, Materials Studio assumes that the rest of the atoms should be treated as a second set. Thus, in the case of a molecule-surface interaction, it is sufficient to create a single set that comprises all the atoms in the molecule.
CASTEP Calculation dialog