How to calculate work function, electron affinity and Schottky barriers

This is a stage by stage guide to how we calculate the band alignment properties of metals and non metals. The example given uses VASP and the key words for doing the calculating in VASP are discussed. Some flags are also discussed as to why do or do not use them. Eventually, it is hoped that the other DFT packages such as crystal17, Quantum Espresso and CASTEP will have links here (no link yet) as to how to do the same proceedure.

The core process

1. Calculate the local potential.

2. Use the eigenvalue file to reference to the potential the last occupied state.

3. For structures with vacuum, use the energy level of the local potential in the empty region to reference the vacuum energy.

4. The difference between these values is the Work function (metals) or hole affinity (insulators).

Details

Band diagrams (as opposed to Band structures) require knowing the relative position of the electronic states to the vacuum level. In periodic systems this is not possible as there is no vacuum, thus making band diagrams somewhat tricky. Instead, the procedure used is to examine what is called the "Local potential."