# Accurate Ionization Potential and Electron Affinity with G0W0¶

Ionization potential (IP) and electron affinity (EA) of molecules can be predicted with reasonable accuracy using the G0W0 method [1] [2].

In this tutorial we will show how to compute the IP and EA of Azulene with ADF using G0W0@PBE0.

## Set up and run the calculation¶

Let’s start by importing the structure of the Azulene molecule from our molecules database:

1. Start AMSinput (SCM → New Input)
2. In the search box search for Azulene and select C10H8: Azulene

Let’s now set up the calculation details in the main panel:

2. XC functional → Hybrid → PBE0
3. Basis set → TZ2P
4. Frozen core → None

To enable the G0W0 calculation:

1. In the panel bar select Properties → G0W0
2. In the G0W0 panel, check the Calculate G0W0 quasi-particle energies checkbox

We are now ready to run the calculation:

1. File → Save and give the job an appropriate name, e.g. “Azulene” (note that symmetry will be automatically disabled for G0W0 calculations)
2. File → Run
3. Wait for the calculation to finish (you can monitor the progress via the logfile, SCM → Logfile)

## Results¶

The results of the calculation are written both to the text output file and to the binary adf.rkf file.

You can use AMSspectra to examine the results from the binary file:

1. SCM → Spectra

To see the G0W0 results in the output file:

1. SCM → Output
2. In AMSoutput, search for “GW” and go the the second hit

The ionization potential (IP) equals the negative of the G0W0 quasi-particle HOMO energy:

$\text{IP} = -\text{HOMO}_{\text{G}_0\text{W}_0} = 7.08 \text{[eV]}$

The electron affinity (EA) equals the negative of the G0W0 quasi-particle LUMO energy:

$\text{EA} = -\text{LUMO}_{\text{G}_0\text{W}_0} = 0.53 \text{[eV]}$

These values are in good agreement with the CCSD(T) results from [1] (IP=7.55 [eV] and EA=0.54 [eV]) and with experimental results cited in [1] (IP=7.42-7.44 [eV] and EA=0.69-0.80 [eV]).

 [1] (1, 2, 3) Joseph W. Knight, Xiaopeng Wang, Lukas Gallandi, Olga Dolgounitcheva, Xinguo Ren, J. Vincent Ortiz, Patrick Rinke, Thomas Körzdörfer, and Noa Marom, Accurate Ionization Potentials and Electron Affinities of Acceptor Molecules III: A Benchmark of GW Methods, J. Chem. Theory Comput. 2016, 12, 2, 615–626
 [2] Arno Förster, Lucas Visscher, Low-order scaling G0W0 by pair atomic density fitting, arXiv.org (2020)