6.2. SCF Stability Analysis

The SCF stability will give an indication whether the SCF solution is at a local minimum or a saddle point.[80, 779] It is available for RHF/RKS and UHF/UKS. In the latter case, the SCF is restarted by default using new unrestricted start orbitals if an instability was detected. For a demonstration, consider the following input:

! BHLYP def2-SVP NORI

%scf
 guess hcore
 HFTyp UHF
 STABPerform true
end

* xyz 0 1 
h 0.0 0.0 0.0
h 0.0 0.0 1.4
*

The HCORE guess leads to a symmetric/restricted guess, which does not yield the unrestricted solution. The same is often true for other guess options. For more details on the stability analysis, see Section SCF Stability Analysis.