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Hartree-Fock Stability Analysis

A HF stability analysis is requested via the keyword HFSTABILITY.

HFSTABILITY=ON

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.

HFSTABILITY=FOLLOW

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

ROT_EVEC=n

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.

Examples

Instability analysis for RHF wavefunctions
Instability analysis for UHF wavefunctions
Determination of a UHF solution for unstable RHF case
Correlated Calculations using symmetry-broken UHF solutions

Recommendations for HF stability analysis calculations