Hello,
Having run a TD-DFT calculation on the Si4GeH12 molecule, we are currently trying to rationalize the results and understand in particular how do the degeneracies of the excited states work.
This is the input file of the calculation:
$molecule 0 1 Si 1.38455 -1.38455 1.38455 Si 1.38455 1.38455 -1.38455 Si -1.38455 1.38455 1.38455 Si -1.38455 -1.38455 -1.38455 Ge -0.00000 -0.00000 -0.00000 H 2.24907 2.24907 -0.54291 H 0.54291 2.24907 -2.24907 H 2.24907 0.54291 -2.24907 H -0.54291 2.24907 2.24907 H -2.24907 0.54291 2.24907 H -2.24907 2.24907 0.54291 H 2.24907 -0.54291 2.24907 H 2.24907 -2.24907 0.54291 H 0.54291 -2.24907 2.24907 H -2.24907 -0.54291 -2.24907 H -2.24907 -2.24907 -0.54291 H -0.54291 -2.24907 -2.24907 $end $rem MEM_TOTAL 2000 JOBTYPE sp EXCHANGE b3lyp BASIS def2-tzvp CIS_N_ROOTS 4 SCF_ALGORITHM diis_gdm SYM_TOL 4 CIS_SINGLETS true CIS_TRIPLETS true CALC_SOC true STS_MOM true PRINT_ORBITALS true MOLDEN_FORMAT true IQMOL_FCHK true $end
And here is the relevant part of the output file:
> ---------------------------------------------------
> TDDFT/TDA Excitation Energies
> ---------------------------------------------------
>
> Excited state 1: excitation energy (eV) = 5.7487
> Total energy for state 1: -3242.16571604 au
> Multiplicity: Triplet
> Trans. Mom.: 0.0000 X 0.0000 Y 0.0000 Z
> Strength : 0.0000000000
> D( 48) --> V( 1) amplitude = 0.7197
> D( 48) --> V( 5) amplitude = -0.2270
> D( 49) --> V( 2) amplitude = 0.4381
> D( 50) --> V( 3) amplitude = -0.4381
>
> Excited state 2: excitation energy (eV) = 5.7487
> Total energy for state 2: -3242.16571604 au
> Multiplicity: Triplet
> Trans. Mom.: 0.0000 X 0.0000 Y 0.0000 Z
> Strength : 0.0000000000
> D( 48) --> V( 2) amplitude = 0.4381
> D( 49) --> V( 1) amplitude = 0.7197
> D( 50) --> V( 4) amplitude = -0.4381
>
> Excited state 3: excitation energy (eV) = 5.7487
> Total energy for state 3: -3242.16571604 au
> Multiplicity: Triplet
> Trans. Mom.: 0.0000 X 0.0000 Y 0.0000 Z
> Strength : 0.0000000000
> D( 48) --> V( 3) amplitude = -0.4381
> D( 49) --> V( 4) amplitude = -0.4381
> D( 50) --> V( 1) amplitude = 0.7197
> D( 50) --> V( 6) amplitude = 0.2484
>
> Excited state 4: excitation energy (eV) = 5.8757
> Total energy for state 4: -3242.16105030 au
> Multiplicity: Triplet
> Trans. Mom.: 0.0000 X 0.0000 Y 0.0000 Z
> Strength : 0.0000000000
> D( 48) --> V( 3) amplitude = -0.5677
> D( 49) --> V( 4) amplitude = 0.5677
> D( 50) --> V( 5) amplitude = -0.5688
>
> Excited state 5: excitation energy (eV) = 5.8757
> Total energy for state 5: -3242.16105030 au
> Multiplicity: Triplet
> Trans. Mom.: 0.0000 X 0.0000 Y 0.0000 Z
> Strength : 0.0000000000
> D( 48) --> V( 2) amplitude = 0.5677
> D( 49) --> V( 5) amplitude = -0.3313
> D( 49) --> V( 6) amplitude = -0.4654
> D( 50) --> V( 4) amplitude = 0.5677
>
> Excited state 6: excitation energy (eV) = 5.8757
> Total energy for state 6: -3242.16105030 au
> Multiplicity: Triplet
> Trans. Mom.: 0.0000 X 0.0000 Y 0.0000 Z
> Strength : 0.0000000000
> D( 48) --> V( 5) amplitude = 0.2374
> D( 48) --> V( 6) amplitude = -0.5197
> D( 49) --> V( 2) amplitude = 0.5677
> D( 50) --> V( 3) amplitude = 0.5677
>
> Excited state 7: excitation energy (eV) = 5.9270
> Total energy for state 7: -3242.15916397 au
> Multiplicity: Triplet
> Trans. Mom.: 0.0000 X 0.0000 Y 0.0000 Z
> Strength : 0.0000000000
> D( 48) --> V( 4) amplitude = -0.5681
> D( 49) --> V( 3) amplitude = -0.5681
> D( 50) --> V( 2) amplitude = 0.5681
>
> Excited state 8: excitation energy (eV) = 6.0509
> Total energy for state 8: -3242.15460988 au
> Multiplicity: Triplet
> Trans. Mom.: 0.0000 X 0.0000 Y 0.0000 Z
> Strength : 0.0000000000
> D( 48) --> V( 3) amplitude = 0.3412
> D( 49) --> V( 4) amplitude = 0.3412
> D( 50) --> V( 1) amplitude = 0.6274
> D( 50) --> V( 6) amplitude = -0.5918
>
> Excited state 9: excitation energy (eV) = 6.0509
> Total energy for state 9: -3242.15460988 au
> Multiplicity: Triplet
> Trans. Mom.: 0.0000 X 0.0000 Y 0.0000 Z
> Strength : 0.0000000000
> D( 48) --> V( 2) amplitude = -0.3412
> D( 49) --> V( 1) amplitude = 0.6274
> D( 49) --> V( 5) amplitude = -0.4843
> D( 49) --> V( 6) amplitude = 0.3448
> D( 50) --> V( 4) amplitude = 0.3412
>
> Excited state 10: excitation energy (eV) = 6.0509
> Total energy for state 10: -3242.15460988 au
> Multiplicity: Triplet
> Trans. Mom.: 0.0000 X 0.0000 Y 0.0000 Z
> Strength : 0.0000000000
> D( 48) --> V( 1) amplitude = 0.6274
> D( 48) --> V( 5) amplitude = 0.5408
> D( 48) --> V( 6) amplitude = 0.2471
> D( 49) --> V( 2) amplitude = -0.3412
> D( 50) --> V( 3) amplitude = 0.3412
>
> Excited state 11: excitation energy (eV) = 6.1093
> Total energy for state 11: -3242.15246491 au
> Multiplicity: Triplet
> Trans. Mom.: 0.0000 X 0.0000 Y 0.0000 Z
> Strength : 0.0000000000
> D( 48) --> V( 4) amplitude = 0.3359
> D( 49) --> V( 3) amplitude = 0.4688
> D( 50) --> V( 2) amplitude = 0.8048
>
> Excited state 12: excitation energy (eV) = 6.1093
> Total energy for state 12: -3242.15246491 au
> Multiplicity: Triplet
> Trans. Mom.: 0.0000 X 0.0000 Y 0.0000 Z
> Strength : 0.0000000000
> D( 48) --> V( 4) amplitude = 0.7353
> D( 49) --> V( 3) amplitude = -0.6586
>
> Excited state 13: excitation energy (eV) = 6.3587
> Total energy for state 13: -3242.14329933 au
> Multiplicity: Singlet
> Trans. Mom.: -0.0000 X -0.5116 Y -0.0000 Z
> Strength : 0.0407751903
> D( 48) --> V( 1) amplitude = 0.8228
> D( 48) --> V( 5) amplitude = -0.3168
> D( 49) --> V( 2) amplitude = -0.3107
> D( 50) --> V( 3) amplitude = 0.3107
>
> Excited state 14: excitation energy (eV) = 6.3587
> Total energy for state 14: -3242.14329933 au
> Multiplicity: Singlet
> Trans. Mom.: -0.5116 X 0.0000 Y -0.0000 Z
> Strength : 0.0407751913
> D( 48) --> V( 2) amplitude = -0.3107
> D( 49) --> V( 1) amplitude = 0.8228
> D( 49) --> V( 5) amplitude = 0.2837
> D( 50) --> V( 4) amplitude = 0.3107
>
> Excited state 15: excitation energy (eV) = 6.3587
> Total energy for state 15: -3242.14329933 au
> Multiplicity: Singlet
> Trans. Mom.: -0.0000 X -0.0000 Y 0.5116 Z
> Strength : 0.0407751956
> D( 48) --> V( 3) amplitude = 0.3107
> D( 49) --> V( 4) amplitude = 0.3107
> D( 50) --> V( 1) amplitude = 0.8228
> D( 50) --> V( 6) amplitude = 0.3467
>
> Excited state 16: excitation energy (eV) = 6.4214
> Total energy for state 16: -3242.14099440 au
> Multiplicity: Singlet
> Trans. Mom.: 0.0000 X 0.0000 Y 0.0000 Z
> Strength : 0.0000000000
> D( 49) --> V( 2) amplitude = 0.7013
> D( 50) --> V( 3) amplitude = 0.7013
>
> Excited state 17: excitation energy (eV) = 6.4214
> Total energy for state 17: -3242.14099440 au
> Multiplicity: Singlet
> Trans. Mom.: 0.0000 X -0.0000 Y -0.0000 Z
> Strength : 0.0000000000
> D( 48) --> V( 2) amplitude = 0.7013
> D( 50) --> V( 4) amplitude = 0.7013
>
> Excited state 18: excitation energy (eV) = 6.4214
> Total energy for state 18: -3242.14099440 au
> Multiplicity: Singlet
> Trans. Mom.: 0.0000 X 0.0000 Y -0.0000 Z
> Strength : 0.0000000000
> D( 48) --> V( 3) amplitude = -0.7013
> D( 49) --> V( 4) amplitude = 0.7013
>
> Excited state 19: excitation energy (eV) = 6.4868
> Total energy for state 19: -3242.13859182 au
> Multiplicity: Singlet
> Trans. Mom.: -0.0000 X -0.0000 Y 0.6058 Z
> Strength : 0.0583334991
> D( 50) --> V( 1) amplitude = 0.4893
> D( 50) --> V( 6) amplitude = -0.8192
>
> Excited state 20: excitation energy (eV) = 6.4868
> Total energy for state 20: -3242.13859182 au
> Multiplicity: Singlet
> Trans. Mom.: -0.6058 X 0.0000 Y -0.0000 Z
> Strength : 0.0583335041
> D( 49) --> V( 1) amplitude = 0.4893
> D( 49) --> V( 5) amplitude = -0.6704
> D( 49) --> V( 6) amplitude = 0.4773
>
> Excited state 21: excitation energy (eV) = 6.4868
> Total energy for state 21: -3242.13859182 au
> Multiplicity: Singlet
> Trans. Mom.: -0.0000 X -0.6058 Y -0.0000 Z
> Strength : 0.0583335053
> D( 48) --> V( 1) amplitude = 0.4893
> D( 48) --> V( 5) amplitude = 0.7485
> D( 48) --> V( 6) amplitude = 0.3420
>
> Excited state 22: excitation energy (eV) = 6.4896
> Total energy for state 22: -3242.13849021 au
> Multiplicity: Singlet
> Trans. Mom.: 0.0000 X 0.0000 Y -0.0000 Z
> Strength : 0.0000000000
> D( 50) --> V( 5) amplitude = -0.9881
>
> Excited state 23: excitation energy (eV) = 6.4896
> Total energy for state 23: -3242.13849021 au
> Multiplicity: Singlet
> Trans. Mom.: 0.0000 X 0.0000 Y -0.0000 Z
> Strength : 0.0000000000
> D( 49) --> V( 5) amplitude = -0.5756
> D( 49) --> V( 6) amplitude = -0.8086
>
> Excited state 24: excitation energy (eV) = 6.4896
> Total energy for state 24: -3242.13849021 au
> Multiplicity: Singlet
> Trans. Mom.: -0.0000 X 0.0000 Y 0.0000 Z
> Strength : 0.0000000000
> D( 48) --> V( 5) amplitude = 0.4124
> D( 48) --> V( 6) amplitude = -0.9028
As you can see, we now have 12 roots (NRoots was altered from 4 to 12) and most, but not all, of the excited states appear to have a 3-fold degeneracy, even the singlets. Is that normal? What might be the rationale behind those results?
Also, in the output file, just before the start of the TDDFT/TDA calculation, I have the following lines which might be related:
> Q-Chem warning in module 0, line 198:
>
> OriOrb: Failure to resolve orbital degeneracies.
But I can’t find anything about this “OriOrb” thing…
Thank you in advance for your help!
Best regards!
Iacobellis Nicolas, Ph.D. Student