In many cases, one wishes to perform a calculation of a low-spin complex where spin-density is positive on some atoms and negative on the others. It is usually very difficult to achieve SCF convergence if one starts from scratch. Sometimes, the MODIFYSTARTPOTENTIAL feature (see next section) helps with this problem but sometimes it does not. A more robust way is to first perform a high-spin calculation and then modify the resulting t21 file by "flipping" the spin on some atoms. This file then can be used to restart a subsequent low-spin calculation.
Such a "flipping" can now be performed during restart by specifying a SPINFLIP keyword in the RESTART input block as shown below:
RESTART high-spin.t21 & ! SpinFlip keyword is followed by atom numbers for ! which the flipping will be performed SPINFLIP 1 END
An example demonstrating the feature may be found in the Examples document.