Keyword FIXMOS

This keyword fixes a molecular orbital configuration by projection during all or part of the SCF.
Options:
FIXED / ITERATIVE

	FIXED		The molecular orbital configuration at the beginning of the projection is used as reference configuration.
	ITERATIVE		The molecular orbital configuration from the preceding SCF cycle is used as reference configuration.
	SCF=$<$Integer$>$		SCF cycle at which the projection procedure is turned on. By default the projection starts with the first SCF cycle.
	TOL=$<$Real$>$		SCF convergence tolerance after which the projection procedure is turned on.

Description:
The projection of the molecular orbital configuration is based on a maximum overlap criterion $\Omega_{ij}$ of the form

$$\Omega_{ij} = \sum_{\mu , \nu} c_{\mu i}^{\rm new} \, S_{\mu \nu} \, c_{\nu j}^{\rm old}%$$ (8)

where $\{c_{\mu i}^{\rm new}\}$ are the new molecular orbital coefficients and $\{c_{\nu j}^{\rm old}\}$ are the ones for the reference configuration. The example input in 4.4.3 shows the application of FIXMOS. The converged MO coefficients and energies clearly show the convergence to an excited state.