Note

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CHARGE

The total electric charge, which specifies the number of electrons in a system. The default charge is zero, corresponding to a number of electrons equal to the total effective nuclear charge on all atoms in the system.

SYNTAX: CHARGE=n

The charge \(n\) must be an integer. Positive values correspond to cations, and negative values correspond to anions.

Use with MOZYME

The CHARGE keyword is compatible with MOZYME calculations, but its behavior changes. MOZYME calculations begin by assigning a Lewis structure to a system, which sets atomic charges and thus a total charge. By default, CHARGE is assigned to the total charge of the Lewis structure. The CHARGE keyword cannot change a system’s total charge in a MOZYME calculation, rather its purpose is to verify that the total charge corresponds to a value that the user expected. By default, a discrepancy in charge values will cause an error, but it can be reduced to a warning with the GEO-OK keyword (the total charge assigned to the Lewis structure is still used in the MOZYME calculation).

When charge conflicts are present, the Lewis structure is printed by MOPAC to assist in the use of other keywords that can adjust the total charge of the Lewis structure to the desired value: METAL to fully ionize specific atoms, SETPI to set explicit double bonds, and CVB to set explicit single bonds or suppress bonds while assiging the Lewis structure.