Vibrationally resolved electronic spectra with ADF
**************************************************

ADF Spectroscopy Franck-Condon (VG-FC) Vibronic-Structure Tracking
(VST) Excited states

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 [image: Search][image] and type "naphthalene" into the box.
   **3.** Select the "Naphthalene (ADF)" entry from the molecules section.
   **4.** Click the Symmetrize button [image: SymmTool][image] 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.** Click the 'Update molecule' button that pops up in the AMSinput window to update the geometry

   [image]


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.
 [image]


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**.
 [image]

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.
