Running Density Functional Theory

A density functional calculation of a solid is always the first step in performing a correlated calculation. The DFT calculation allows you to understand global aspects of the band structure, compare to reference literature results, and get a general feeling for the problem. DFT codes are mature and foolproof.

Step 1 – Vasp with PBE

The Vienna Ab-Initio Simulation Package VASP is a good place to get started for standard DFT. Codes are installed on Pauli but running VASP requires you to be a registered user, please contact Dominika to make sure that you are. Following the guidelines at the VASP homepage, make sure that you can obtain the band structure of your compound of interest. VASP is a plane-wave code, meaning that its results will not be influenced by your choice of basis. PBE is a very standard functional and a decent initial choice of functional.

Runxue gave an introduction to VASP in our group seminar

Step 2 – Crystal or CP2K with PBE

Next step in the workflow consists of running the same crystal in CP2K or Crystal. Both of these packages are established Gaussian codes, Crystal is very fast and implements symmetries efficiently but is somewhat limited with pseudopotentials, while CP2K is a more established standard Gaussian DFT code. Gaussian bases are differently biased from plane wave basis sets with pseudopotential. Obtaining a bandstructure plot in both codes will give you a basis for comparison. Yanbing gave an excellent tutorial on using Crystal.

Step 3 – DFT in pySCF

In a third step, you will repeat the calculation that you just did in VASP and Crystal in PySCF. DFT in pySCF is much more primitive than in the established DFT packages, and checking the DFT results against established codes will give confidence in your setup, which we will then use for diagrammatic calculations.