Tutorials

Periodic systems have always been the primary application for DFT+U. The original utility of DFT+U was largely observed in improving descriptions of band gaps and recovering insulating behavior in materials that standard approximations to DFT make metallic.

Multiple low-lying electronic states are common for open-shell transition metal complexes and other small molecules. It is important to make sure you can straightforwardly characterize each state you converge to in order to be certain you are obtaining the properties you wish to calculate.

Thus far, I’ve told you about how to calculate the Hubbard U for single sitesor multiple sites and how to troubleshoot common problems with DFT+U. In fact, calculating U is nearly as easy as carrying out a single point calculation.

Thus far, I have introduced how to calculate U from linear-response for both single-site and multiple-site systems. However, there are a few practical issues you may run into when using DFT+U to study your system.

Open shell species of any kind may have a number of different low-lying electronic states that are all self-consistent solutions. Even though DFT is a ground state method, it may be applied directly to the lowest electronic state with well-defined quantum numbers, i.

The nudged elastic band approach for identifying transition-states is implemented in Quantum-ESPRESSO and in version, 4.3.1, it can be driven by electronic structure results from either CP or PWscf. A basic example of how to use this approach is provided in #17 of the examples that are distributed with the code.

Have you ever run a relaxation or a path optimization technique (e.g. nudged elastic band or string metadynamics) on an isolated system only to find that you were getting spurious answers arising from rotation or translation of your system?

This tutorial is suited to those interested in carrying out DFT+U calculations on a system with multiple transition-metal sites. If, instead, you are only concerned with single-site complexes, check out the original tutorial on calculating the Hubbard U.

After we’ve completed a few simulations, it can be very useful to visualize the electronic structure of our system. In Quantum-ESPRESSO, the wavefunctions we collect at the end of a calculation can be postprocessed for visualization of a number of properties including: the total density, spin density, and density of each molecular state.

If you you think you might be interested in carrying out DFT+U calculations on a system, this tutorial is tailor made for you.  Background: Recall, the DFT+U functional, as implemented in Quantum-ESPRESSO[1] corresponds to an additional term of the form: