in QM/MM calculations it is usually more convenient to read in the point charges from a file (see below). When many point charges are present, e.g. Note that when adding point charges as " Q " atoms, the self-interaction between point charges is calculated and included in the final energy. Point charges in an ORCA calculation are basically handled in the same way as nuclear charges. A point charge has no electrons or basis functions but has a fixed charge which may be negative or positive. Point charges can also easily be added by both specifying the charge and coordinates and using the symbol " Q ". Ghost atoms are typically used in the counterpoise procedure to correct for basis set superposition error (BSSE). A ghost atom has no electrons or nucleus but has basis functions assigned. Ghost atoms: Make an atom a ghost atom by adding " : " after its element symbol. It has no charge or electrons or basis functions. Dummy atoms are not real atoms, they have no electrons, nucleus or basis functions. Sometimes one wants to add additional non-standard parts to the coordinate block i.e dummy atoms.ĭummy atoms: Use " DA " as a symbol and the appropriate coordinates. Dummy atoms, ghost atoms, point charges etc.
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