DFT + GWBSE Optimization Using CO

Introduction

This tutorial explains how to perform a molecular geometric optimization using the GWBSE method. See the GW Compendium: A Practical Guide to Theoretical Photoemission Spectroscopy, for an excellent introduction to the method.

Requirements

  • You will need to install VOTCA using the instructions described here

  • Once the installation is completed you need to activate the VOTCA enviroment by running the VOTCARC.bash script that has been installed at the bin subfolder for the path that you have provided for the installation step above

Preparing the input

To run a DFT-GWBSE calculation we will use the xtp_tools calculator.

we can now change the calculator mode from single point energy calculation to optimization as follows by adding -c geometry_optimization.maxiter=1 which enables optimization with one iteration.

Because geometry optimsation is quite expensive numerically we chose a smaller basisset and G0W0 Finally, to run the calculation we just need the following command (This still takes a while)

[1]:
!xtp_tools -c job_name=CO geometry_optimization.maxiter=1 dftpackage.basisset=3-21G dftpackage.auxbasisset=aux-def2-svp gwbse.gw.mode=G0W0 -e dftgwbse -t 4
/bin/sh: 1: xtp_tools: not found

Notice that we are using 4 threads. The results will be stored in a file named CO_summary.xml in the current work directory, together with the optimization step in optimisation.trj and the orbitals in hdf5 format saved on CO.orb.