RHF open-shell derivatives are normally calculated using Liotard's analytical C.I. method . In general, do not use NOANCI (NO ANalytical Configuration Interaction derivatives). NOANCI should only be used if there is cause to believe that the derivatives are faulty, because it evaluates the gradient using finite differences involving complete SCF calculations. In contrast, Liotard's method is very fast, so using NOANCI will cause the job to take much longer than if NOANCI were not used.
In the unusual situation when analytical C.I. derivatives are not to be used, specify NOANCI. See also GRADIENTS.