Previously, the spin-contamination correction was done for the complete system, but starting from version 2009.01 it can be performed for different regions, as in the following example:
QUILD
DESCRIPTION 1 ADF
Occupations smearq=0.0 &
AA1 4.0 // 5.0
AA2 0.0 // 0.0
EE1 8.0 // 8.0
EE2 6.0 // 4.0
AAA1 0.0 // 0.0
AAA2 4.0 // 4.0
EEE1 6.0 // 6.0
EEE2 4.0 // 4.0
End
CHARGE 0.0 1.0
Unrestricted
SUBEND
DESCRIPTION 2 ADF
Occupations smearq=0.0 &
AA1 5.0 // 4.0
AA2 0.0 // 0.0
EE1 8.0 // 8.0
EE2 6.0 // 4.0
AAA1 0.0 // 0.0
AAA2 4.0 // 4.0
EEE1 6.0 // 6.0
EEE2 4.0 // 4.0
End
CHARGE 0.0 3.0
Unrestricted
SUBEND
INTERACTIONS
TOTAL description 1
S2CORR region 1 spin-splus-description 2 for contaminated-description 1
SUBEND
END
SYMMETRY D(5H)
Note that this in this case, the spin-contaminated system (doublet) consists of a triplet-alfa in the EE2-irrep coupled with a doublet-beta in the AA1-irrep. This is corrected for by a pure quartet, and the corresponding energies corrected:
Values for S2correction 1 : s2cont 1.75396 s2pure 0.75000 s2plus 3.78716 a_s2 0.33056 jobsigns job 2 -0.49378 job 1 1.49378
