Keyword MOMODIFY

This keyword modifies the molecular orbital occupation.
Options:

	$<$Integer1$>$		Number of $\alpha$ molecular orbital occupation modifications.
	$<$Integer2$>$		Number of $\beta$ molecular orbital occupation modifications.

Description:
The modified molecular orbital occupations are read in the keyword body of MOMODIFY, one line for each modification. Such a modification consists of an integer number that specifies the molecular orbital to be modified and a real number for the molecular orbital occupation. First all $\alpha$ MO modifications are read, and then, in the case of an unrestricted or spin-restricted open-shell calculation (see 4.5.1) $\beta$ MO modifications are read. At most 10 molecular orbitals of each spin manifold can be modified. The following He atom input modifies the $\beta$ occupation of orbital 1 to 0.75.

 PRINT MOS
 SCFTYPE UKS
 MOMODIFY 0 1
 1 0.75
 GEOMETRY CARTESIAN ANGSTROM
 He 0.0 0.0 0.0

Note that the MULTIPLICITY keyword (see 4.4.1) refers to the unmodified system, i.e. without fractional MO occupation. The fractional MO occupation can be best monitored by printing the molecular orbitals. We find for the above He atom input after SCF convergence:

 ALPHA MO COEFFICIENTS OF CYCLE 6

                                1          2
                            -0.7814     0.3711

                             1.0000     0.0000

     1    1  He    1s        0.8294    -0.9999
     2    1  He    2s        0.2402     1.2768


 BETA MO COEFFICIENTS OF CYCLE 6

                                1          2
                            -0.7342     0.3936

                             0.7500     0.0000

     1    1  He    1s        0.8089    -1.0166
     2    1  He    2s        0.2661     1.2716

As this output shows the 0.75 occupation of the $\beta$ MO breaks the energy degeneracy of the $\alpha$ and $\beta$ MOs. Also the MO coefficients are different. To obtain total energies that match with integer occupied calculations, e.g. for the cation or anion, the UKS SCFTYPE (see 4.5.1) option must be selected!