# Simulate UV-Vis spectra using SF-TDDFT

Hello everyone, I am curious if it is possible to simulate UV-Vis spectra using SF-TDDFT methods in Q-Chem?

In principle one may simulate a UV/Vis spectrum using any method that provides electronic excitation energies, which SF-TDDFT does. Beyond that, you would need to be more specific.

I guess the thing thatâ€™s slightly tricky is that you have to specify a reference state for the oscillator strengths. But I am sure the TDDFT module would give you state-to-state osc strengths

Dear John and Felix,
I have problem with oscillator strengths and their corresponding excitation energies.
Considering the output example below, if we assume that the first excitation represents the ground state, would it be correct to subtract 0.3065 from all subsequent excitation energies?

`````` ---------------------------------------------------
SF-DFT Excitation Energies
(The first "excited" state might be the ground state)
---------------------------------------------------

Excited state   1: excitation energy (eV) =    0.3065
Total energy for state  1:                 -1318.13996799 au
<S**2>     :  0.8258
S(  1) --> S(  1) amplitude = -0.2621 alpha
S(  1) --> V(  1) amplitude =  0.9432 alpha

Excited state   2: excitation energy (eV) =    1.3046
Total energy for state  2:                 -1318.10328898 au
<S**2>     :  0.7914
S(  1) --> S(  1) amplitude =  0.9366 alpha
S(  1) --> V(  1) amplitude =  0.2499 alpha

Excited state   3: excitation energy (eV) =    1.9528
Total energy for state  3:                 -1318.07946979 au
<S**2>     :  0.8128
S(  1) --> V(  4) amplitude =  0.1624 alpha
S(  1) --> V(  5) amplitude = -0.2227 alpha
S(  1) --> V(  6) amplitude =  0.8386 alpha
S(  1) --> V(  8) amplitude = -0.1770 alpha
S(  1) --> V(  9) amplitude =  0.3062 alpha

``````

Furthermore, am I correct in utilizing the oscillator strengths provided when STS_MOM = True, as shown in the following output?

``````                Transition Moments Between Excited States
--------------------------------------------------------------------------------
States   X          Y          Z           Strength(a.u.)
--------------------------------------------------------------------------------
1    2   0.212699  -0.028354   0.631931     0.01089077
1    3  -0.732231  -0.004565   0.153223     0.02257232
1    4  -0.015078   0.034331  -0.129219    0.001038044
1    5   0.247993   0.104720   0.092854    0.004731557
1    6   0.020002  -0.499355  -0.014295     0.01530406
1    7   1.427047   0.230422  -0.028827      0.1344544
1    8   0.828349   0.205192  -0.061805     0.04811119
1    9   0.396399  -1.535277  -0.076765      0.1664617
1   10  -0.157090  -0.377781  -0.054275      0.0117728
1   11  -0.156061  -0.002681  -0.023635    0.001814344
1   12  -0.015027   0.360521  -0.006755    0.009887001
1   13   0.184101   0.317657   0.042908     0.01050708
1   14   0.006168   0.045406  -0.073119    0.000593253
1   15   0.001179   0.400377   0.049055     0.01352052
1   16   0.022781  -0.425961  -0.057250     0.01576211
1   17   0.121259   0.030317  -0.114453    0.002481538
1   18   0.010137   0.438371   0.011766     0.01690756
1   19  -0.126662   0.041931   0.200451    0.005302814
1   20   0.366314  -0.274850  -0.027304     0.01938061
2    3   0.236713   0.035481  -1.380810     0.03118613
2    4   2.184189   1.978248  -0.008149       0.285595
2    5  -1.979458   2.101363   0.100918      0.2828494

``````

First point is correct, first excitation energy is between the reference state and the ground state of the target multiplicity.

State-to-state oscillator strengths are probably okay but I might verify in a simple case where you can compare again normal spin-conserving TDDFT.

The ezFCF package will be helpful for adding vibrational progressions to the spectra