Description
SHIFT is useful in obtaining an SCF in situations where oscillations (sometimes
attributed to autoregenerative charge fluctuations) are hindering or preventing convergence of
the wavefunction. This is accomplished by raising the virtual (unoccupied) and singly occupied
MOs in energy relative to the occupied set, thus decreasing the polarizability of the occupied
MOs. The value specified as n.n is the energy offset in eV. Note that a dynamic shift
algorithm has been added to the “emergency” covergence suite (see
Chapter 4, Computational Procedures). As the SCF approaches convergence, the SHIFT is
gradually decreased. As some virtual MOs are used in non-variationally optimized calculations,
SHIFT is automatically annulled at the end of the SCF in these circumstances. All effects of
SHIFT are removed before results are printed. Caution: Use of the SHIFT method may cause
slower SCF convergence.
