17.9.1 Level shifts

SHIFT,shifta,shiftb,nitord,nitcl,nitocc

A level shift of shifta and shiftb hartree for $\alpha$- and $\beta$-spin orbitals, respectively, is applied. This can improve convergence, but has no effect on the solution. shifta$=-0.2$ to $-0.3$ are typical values. The defaults are shifta$=0$ and shifta$=-0.3$ in closed and open-shell calculations, respectively, and shiftb$=0$.

In open-shell calculations, the orbitals are reordered after each iteration to obtain maximum overlap with the orbitals from the previous iteration. This takes only effect after nitord iterations. The default is nitord$=$maxit$/4$ if no start card is present and nitord$=1$ if a START card is found.

Starting with iteration nitocc the occupation pattern is kept fixed. The default depends on the quality of the starting guess.

If the iteration count is smaller than nitcl, only the closed-shell part of the Fock matrix is used (default nitcl$=0$).