SCFCRT sets the self-consistent field criterion, i.e., the change in energy in kcal/mol on two successive iterations. For most situations where the SCF criterion need to be modified, use RELSCF instead.  RELSCF is useful if the value of the default SCF criterion is not readily available, as for example when PRECISE or any other keywords that modify the SCF criterion is used. The default SCF criterion,1x10-4 kcal/mol, is to be replaced by that defined by SCFCRT=n.nnn.  Other criteria may make the requirements for an SCF slightly more stringent. The SCF criterion can be varied from about 1.0 to 1.D-25, although numbers in the range 0.1 to 1.D-9 will suffice for most applications.

In FORCE, NLLSQSIGMA, or TS calculations, the default value of SCFCRT is 1x10-7. Be careful in FORCE calculations - high precision is needed, if high precision is not used, the vibrational frequencies might be wrongly predicted.

An overly tight criterion can lead to failure to achieve an SCF, and the consequent failure of the run.  See also RELSCF and PRECISE