Hello,

We are currently trying to understand the link between the SOC obtained through TD-DFT calculations and the symmetry of our molecules. Right now, we are comparing Si5H12 and Si4GeH12, both with Td symmetry.

What is of particular interest to us are the symmetries of the triplet excited states T1, T2 and T3. For both Si5H12 and Si4GeH12, as far as our understanding goes, those states should have the orbital symmetry T2, which means their SOC value with the ground state should be greater than zero, since the ground state has the orbital symmetry A1. But when we look at the value given by Q-CHEM, it doesnâ€™t look to match what we have for Si4GeH12.

*Si5H12*

```
Total SOC between the singlet ground state and excited triplet states:
T1 10.900458 cm-1
T2 10.900458 cm-1
T3 10.900458 cm-1
```

*Si4GeH12*

```
Total SOC between the singlet ground state and excited triplet states:
T1 0.000002 cm-1
T2 0.000002 cm-1
T3 0.000000 cm-1
```

Here are the input files for each calculation:

*Si5H12*

```
$molecule
0 1
Si 1.360840033313 -1.360840033313 1.360840033313
Si 1.360840033313 1.360840033313 -1.360840033313
Si -1.360840033313 1.360840033313 1.360840033313
Si 0.000000000000 0.000000000000 0.000000000000
Si -1.360840033313 -1.360840033313 -1.360840033313
H 2.226738754740 -0.522677561432 2.226738754740
H 2.226738754740 -2.226738754740 0.522677561432
H 0.522677561432 -2.226738754740 2.226738754740
H 2.226738754740 2.226738754740 -0.522677561432
H 0.522677561432 2.226738754740 -2.226738754740
H 2.226738754740 0.522677561432 -2.226738754740
H -0.522677561432 2.226738754740 2.226738754740
H -2.226738754740 0.522677561432 2.226738754740
H -2.226738754740 2.226738754740 0.522677561432
H -2.226738754740 -0.522677561432 -2.226738754740
H -2.226738754740 -2.226738754740 -0.522677561432
H -0.522677561432 -2.226738754740 -2.226738754740
$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
IQMOL_FCHK true
$end
```

*Si4GeH12*

```
$molecule
0 1
Si 1.387052972184 -1.387052972184 1.387052972184
Si 1.387052972184 1.387052972184 -1.387052972184
Si -1.387052972184 1.387052972184 1.387052972184
Si -1.387052972184 -1.387052972184 -1.387052972184
Ge 0.000000000000 0.000000000000 0.000000000000
H 2.251918652130 2.251918652130 -0.548031589165
H 0.548031589165 2.251918652130 -2.251918652130
H 2.251918652130 0.548031589165 -2.251918652130
H -0.548031589165 2.251918652130 2.251918652130
H -2.251918652130 0.548031589165 2.251918652130
H -2.251918652130 2.251918652130 0.548031589165
H 2.251918652130 -0.548031589165 2.251918652130
H 2.251918652130 -2.251918652130 0.548031589165
H 0.548031589165 -2.251918652130 2.251918652130
H -2.251918652130 -0.548031589165 -2.251918652130
H -2.251918652130 -2.251918652130 -0.548031589165
H -0.548031589165 -2.251918652130 -2.251918652130
$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
IQMOL_FCHK true
$end
```

Just in case, here are the output files (it is too long to just paste it here so I had to rely on a third-party website)

Si5H12 : https://file.io/gjCdjCysdwxd

Si4GeH12: https://file.io/hooUIB7sM7WB

Are we missing something?

On another, related note, since we are also working with bigger molecules where doing symmetry analysis by hand will prove to be a bit tiresome, **is there a way to obtain the electronic configuration of the excited states**?

Thank you for your help!

Iacobellis Nicolas, PhD. Student