Specifies that the geometry is to be taken from the checkpoint file and that modifications will be made to it. A total of two input sections will be read: the first contains the charge and multiplicity, and the second contains alterations to the retrieved geometry.
Modification specifications for geometry optimizations using Z-matrix coordinates have the following form:
variable [new-value] [A|F|D]
where variable is the name of a variable in the molecule specification, new-value is an optional new value to be assigned to it, and the final item is a one-letter code indicating whether the variable is to be active (i.e., optimized) or frozen; the code letter D requests numerical differentiation be performed with respect to that variable and activates the variable automatically. If the code letter is omitted, then the variable¡¯s status remains the same as it was in the original molecule specification.