Introduction

This tutorial was given in October 2014 at the CECAM Workshop on High Performance Models for Charge Transport in Large Scale Materials Systems at the Bremen Center for Computational Materials Science in Bremen, Germany. It demonstrates some of the possible uses of the DFTB+ code for calculating geometries, electronic structures and electron transport properties of various 2D carbon materials. It is aimed at Master and starting PhD-students with background knowledge of the theory of electronic structure and electron transport. Minimal knowledge of Unix is also required. Knowledge of the DFTB+ code itself is not necessary, but familiarity with the basic ideas behind the Density Functional Tight Binding (DFTB) method could be helpful.

System environment

The easiest way to use this tutorial is to download the live ISO image, which contains a preconfigured X86_64/Linux system with all the necessary tools for the tutorial. One can directly boot the ISO image within a virtual machine (e.g. VirtualBox). Alternatively, one can create a bootable USB-drive (e.g. with usb-creator under Linux or Universal USB Installer under Windows) or DVD, which can then be used to boot up an X86_64 machine with the live system.

When you start the image, please select the default language (English). Then you may press the F3 key, to select a keyboard layout of your choice, otherwise the default one (US) will be used. Finally, select the first menu (Trying Lubuntu ...) to boot the system.

In case you want to try the tutorial outside of the live system, you will need the following tools to be installed:

  • dftb+ – DFTB+ binary (version 1.2.2).
  • dftb+negf – Parallel DFTB+ with Non-Equilibrium Greens function extension.
  • Parametrisation set mio-1-1.
  • waveplot – Command line tool to create volumetric data files representing electron densities and wavefunctions.
  • leafpad – A simple graphical text editor. You can alternatively use your preferred editor instead.
  • gen2xyz, dp_dos, dp_bands – Various conversion scripts from the dp_tools package.
  • repeatgen – Repeats periodic GEN format along lattice vectors. You can just copy the script from the live image, as it is a standalone program.
  • Jmol – Graphical molecular visualisation tool. You can alternatively use any molecular visualiser able to plot volumetric data and isosurfaces.

General notes

  • The working directory of each of the tutorial examples is indicated at the beginning of its corresponding section. Please change to that directory and execute the specified commands from within that directory.
  • It is impossible to describe all options accepted by DFTB+ within the tutorial. Always make sure, that you understand the input file for DFTB+ (dftb_in.hsd). If you find any unexplained options, consult the DFTB+ documentation page for details.
  • In order to save you some typing, many of the necessary commands have been already collected into small scripts. Please have a look at the content of these scripts before executing them, making sure you understand why those commands must be executed in that order to obtain the necessary results.
  • The special version of the DFTB+ code and the parametrisation data in this tutorial can be freely used for educational purposes. If you would like to obtain a regular (academic or commercial) licensed copy of the code and/or the parametrisation data for your research, please consult the website of the DFTB+ program package and of the parametrisation data. The regular version of the DFTB+ code and the parametrisation data is available free of charge for academic, educational and non-profit usage.