Hello every one.I am a beginner in computational chemistry field.Just for a learning exercise I want to generate a singlet delta(g) state of a dioxygen using SF-TDDFT method on a triplet sigma(g) (-) reference state in QChem. The input I am giving is following:

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$MOLECULE
0 3
O 0.00000000 0.00000000 0.60746100
O 0.00000000 0.00000000 -0.60746100
$END

$rem
jobtype = sp
UNRESTRICTED =TRUE
scf_guess = core
EXCHANGE = b3lyp
BASIS = cc-pVTZ
SPIN_FLIP = 1
CIS_N_ROOTS = 2
SET_STATE_DERIV = 2
max_cis_cycles = 100
$end

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The output which Qchem gives me (Part of the output) is following:

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9 -150.3808246907 4.76E-08
10 -150.3808246907 5.61E-09 Convergence criterion met
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<S^2> = 2.0083
SCF time: CPU 4.91 s wall 5.27 s
SCF energy in the final basis set = -150.3808246907
Total energy in the final basis set = -150.3808246907
Spin-flip DFT calculation will be performed
CIS energy converged when residual is below 10e- 6
NRoots was altered as: 2 --> 4
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Iter Rts Conv Rts Left Ttl Dev Max Dev
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1 0 4 0.005819 0.001581
2 0 4 0.000180 0.000060
3 1 3 0.000004 0.000001
4 4 0 0.000001 0.000000 Roots Converged
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SF-DFT Excitation Energies
(The first "excited" state might be the ground state)
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Excited state 1: excitation energy (eV) = 1.8613
Total energy for state 1: -150.312421537588
<S**2> : 2.0141
Trans. Mom.: -0.0002 X 0.3773 Y 0.0002 Z
Strength : 0.0065
S( 1) --> S( 1) amplitude = 0.7064 alpha
S( 2) --> S( 2) amplitude = 0.7064 alpha

Excited state 2: excitation energy (eV) = 2.1170
Total energy for state 2: -150.303026618401
<S**2> : 0.0107
Trans. Mom.: -0.0001 X -0.3746 Y -0.0017 Z
Strength : 0.0073
S( 1) --> S( 1) amplitude = -0.7065 alpha
S( 2) --> S( 2) amplitude = 0.7065 alpha

Excited state 3: excitation energy (eV) = 2.1170
Total energy for state 3: -150.303026438419
<S**2> : 0.0107
Trans. Mom.: -0.0013 X -0.1130 Y -0.0006 Z
Strength : 0.0007
S( 1) --> S( 2) amplitude = 0.7065 alpha
S( 2) --> S( 1) amplitude = 0.7065 alpha

Excited state 4: excitation energy (eV) = 2.3796
Total energy for state 4: -150.293376152658
<S**2> : 0.0106
Trans. Mom.: 0.0000 X 0.1135 Y 0.0000 Z
Strength : 0.0008
S( 1) --> S( 2) amplitude = 0.7067 alpha
S( 2) --> S( 1) amplitude = -0.7067 alpha

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Total time for CIS 2.35s
Total time for CIS 0.00s
Total time for CIS 2.37s
Analysis of SCF Wavefunction

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I think the Excited state 1( <S**2> : 2.0141) is the Triplet State with Ms=0.The Singlet state(<S**2> : 0.0107) is clearly multireference .This singlet state seems to be the Singlet Delta(g) . The Energy gap between the reference Triplet state and the Singlet Delta(g) is =(-150.303026618401+-150.3808246907)*627.51=48.8 KCal does not matches with the literature value(22.4 KCal).Though with CASSCF level of theory I am able to be close enough the literature value.Am I doing completely wrong???Is there any input errors??Or I am wrong in analyzing the output file??



Please help me out...

Thanks in advance,

Gaurab Ganguly