Vibrationally resolved electronic spectra with ADF¶

In this tutorial we use the vertical gradient Franck-Condon (VG-FC) Vibronic-Structure Tracking (VST) method to calculate the vibrationally resolved absorption spectrum of the first excited singlet state of naphthalene.

There are different methods to calculate a vibrationally resolved absorption spectrum. Out of these methods VST is in principal the quickest method and can also be used for much larger sized molecules. It is based on a mode-tracking algorithm and works by tracking those modes that are expected to have the largest impact on the vibronic-structure of the spectrum. More information on VST and related methods can be found in the AMS user manual:

• Vibrationally resolved electronic spectra section of the AMS manual

Step 1: Geometry Optimization¶

Let us first obtain a naphthalene molecule, and optimize its geometry with ADF.

1. Start AMSinput.

2. In AMSinput, click the search icon and type “naphthalene” into the box.

3. Select the “Naphthalene (ADF)” entry from the molecules section.

4. Click the Symmetrize button to check the symmetry (should be D(2H))

5. Select Task → Geometry Optimization.

6. Select Frozen core → None.

7. Click on File → Save As… and give it the name “naphthalene_GO”.

8. Click on File → Run.

9. Wait for the calculation to finish.

10. When AMSinput asks if it should update the geometry to the optimized geometry, select Yes.

Step 2: Excited state gradient¶

Here we will look at the vibrationally resolved absorption spectra of the lowest electronically excited singlet state S1. The VG-FC Vibronic-Structure Tracking method needs the excited state gradient of S1 at the ground state geometry.

See also

ADF manual sections on excitations and excited states gradients

Select Task → Single Point.

Panel bar Properties → Gradients, Stress tensor.

Check the Nuclear gradients checkbox.

Panel bar Properties → Excitations (UV/Vis), CD.

Select Type of excitations → SingletOnly.

Enter ‘1’ for Number of excitations.

Panel bar Properties → Excited State Geometry.

Check the All Gradients checkbox.

Click on File → Save As… and give it the name “naphthalene_ES”.

Click on File → Run.

Wait for the calculation to finish.

Step 3: Vibronic-Structure Tracking¶

The calculated lowest excited singlet state is of B2.u symmetry. For the VG-FC vibronic-structure tracking method we need a new input:

Click on SCM → New Input.

Click on File → Import Coordinates… and and select the “naphthalene_ES.ams” file.

Select Task → Vibrational Analysis.

Select Frozen core → None.

Panel bar Model → Vibrational Analysis.

Select Type → Vibronic Structure Tracking.

Panel bar Details → Vibrational Analysis… → Vibrational Analysis Excitation.

Click on the folder next to Excitation file: and select the file adf.rkf in the folder naphthalene_ES.results

Enter ‘B2.u 1’ for Singlet.

Panel bar Details → Vibrational Analysis… → Vibrational Analysis Spectrum.

Enter ‘50’ for Line width in cm^-1.

Click on File → Save As… and give it the name “naphthalene_VST”.

Click on File → Run.

Wait for the calculation to finish (may take several minutes).

Click on SCM → Spectra.

The spectrum is relative to the 0-0 excitation energy. The default (artificial) broadening is relatively wide, therefore it was changed to 50 cm^-1.