Hartree-Fock Stability Analysis
A HF stability analysis is requested via the keyword HFSTABILITY.
just requests a stability check (real RHF instabilities, real UHF instabilities, as well as magnetic RHF/UHF instabilities) and provides lowest eigenvalues and eigenvectors for the corresponding orbital hessians.
requests a stability analysis followed (in the case of a instability) by HF-SCF calculations searching for a lower solution. Note that these calculations should be performed with REF=UHF and SYM=OFF, as otherwise this SCF calculations cannot be properly performed. Default is here to follow the eigenvectors to the lowest eigenvalue of the orbital hessian, but use of higher-lying negative eigenvectors can be enforced via
where n specifies the corresponding eigenvector to be followed.
Note that a HF stability analysis can be combined with a correlated calculation and also be used to provide symmetry-broken UHF solutions.