Resonance Raman
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ADF Spectroscopy Franck-Condon (VG-FC) resonance Raman Excited states

In this tutorial we use the vertical gradient Franck-Condon (VG-FC)
resonance Raman method to calculate a resonance Raman spectrum in
which the incident photon energy is close in energy to one of the
excited singlet states of pyrene.

The VG-FC resonance Raman application needs all ground state
vibrational frequencies and the electronically excited state gradient
of the excited state of interest calculated at the ground state
geometry. More information on how resonance Raman is calculated in the
VG-FC method can be found in the AMS user manual:

* VG-FC resonance Raman section of the AMS manual

Let us first obtain a pyrene molecule. We optimize its geometry and
calculate the vibrational frequencies with DFTB.

   Start AMSjobs.
   Click on **SCM → New Input**. This will open AMSinput.
   In AMSinput, click the search icon [image: Search][image] and type "pyrene" into the box.
   Select the "Pyrene (ADF)" entry from the molecules section.
   Click the Symmetrize button [image: SymmTool][image] to check the symmetry (should be D2h).
   Select the DFTB panel: [image: ADFPanel][image] **→** [image: DFTBPanel][image].
   Check the **Frequencies** checkbox.
   Select **Model → DFTB3**.
   Select **Parameter directory → DFTB.org/3ob-3-1**.

   Click on **File → Save As...** and give it the name "pyrene_IR".
   Click on **File → Run**.
   Wait for the calculation to finish.
   Click the 'Update molecule' button that pops up in the AMSinput window to update the geometry.
   Click on **SCM → Spectra**.
 [image]

We calculate the excited state gradient of the lowest 11 excited
states at the ground state geometry. This should give us multiple
dipole-allowed excitations, allowing us to analyze different resonance
modes.

   Click on **SCM → New Input**.
   Click on **File → Import Coordinates (System) → From Files(s)** and and select the "pyrene_IR.results/dftb.rkf" file.
   Select the DFTB panel: [image: ADFPanel][image] **→** [image: DFTBPanel][image].
   Select **Task → Single Point**.
   Select **Model → DFTB3**.
   Select **Parameter directory → DFTB.org/3ob-3-1**.

   Panel bar **Properties → Gradients, Stress Tenor**.
   Check the **Nuclear gradients** checkbox.

   Panel bar **Properties → Excitations (UV/Vis)**.
   Select **Type of excitations → Singlet**.
   Enter '20' for **Number of excitations**.
   Enter '1 2 3 4 5 6 7 8 9 10 11' for **Calculate excited state gradients for Excitation number**.

   Click on **File → Save As...** and give it the name "pyrene_ES"
      (in the directory in which pyrene_IR.ams was saved).
   Click on **File → Run**.
   Wait for the calculation to finish.
   Click on **SCM → Spectra**.
   **Axes → Horizontal Unit → eV**.
   **Width → 0.01**.
 [image]

   **Axes → Horizontal Unit → cm-1**.

The dipole allowed excitations are number 1, 2, 5, and 11. First we
calculate a resonance Raman spectrum in which the incident photon is
close in energy to the calculated lowest excited state at around 26000
cm^-1. For the VG-FC resonance Raman method we need a new input:

   Click on **SCM → New Input**.
   Click on **File → Import Coordinates (System) → From Files(s)** and and select the "pyrene_ES.ams" file.
   Select the DFTB panel: [image: ADFPanel][image] **→** [image: DFTBPanel][image].
   Select **Task → Vibrational Analysis**.
   Select **Model → DFTB3**.
   Select **Parameter directory → DFTB.org/3ob-3-1**.

   Panel bar **Model → Vibrational Analysis**.
   Select **Type → Resonance Raman**.
   Click on the folder next to **Mode file:** and select pyrene_IR.results/dftb.rkf.
   Check the **All modes** checkbox.

   Click on the [image: MoreBtn][image] next to **Excitation Settings**.
   Click on the folder next to **Excitation file** and select pyrene_ES.results/dftb.rkf.
   Enter 'A 1 2 5 11' for **Singlet**.

   Click on the [image: LessBtn][image] to go back to the previous page.
   Click on the [image: MoreBtn][image] next to **Spectrum Settings**.
   Enter '26000' for **Incident Frequency** in cm^-1.

   Click on **File → Save As...** and give it the name "pyrene_RR".
   Click on **File → Run**.
   Wait for the calculation to finish.
   Click on **SCM → Spectra**.
   Set the **Width** to 20 cm^-1.
 [image]

The peaks in the spectrum are at frequencies that correspond to
fundamental vibrations (IR frequencies), combination bands (sum of
different IR frequencies) and overtones (sum of identical IR
frequencies). The default Raman order is 2, which means that the
summation is over a maximum of 2 IR frequencies. AMSspectra gives a
list of frequencies and Raman intensities and the corresponding mode
numbers of the IR frequencies involved. For fundamental frequencies
only 1 mode number is shown. The mode numbers correspond to the
numbers in an energy-ordered list of IR frequencies.

Next we calculate a resonance Raman spectrum in which the incident
photon is close in energy to the calculated 11th excited state at
around 40000 cm^-1.

   Click on **SCM → Input** (go back to the Input window).

   Panel bar **Details → Vibrational Analysis Spectrum**.
   Enter '40000' for **Incident Frequency** in cm^-1.

   Click on **File → Save As...** and give it the name "pyrene_RR_11".
   Click on **File → Run**.
   Wait for the calculation to finish.
   Click on **SCM → Spectra**.
   Set the **Width** to 20 cm^-1.
 [image]
