tgmaxson / castep-linear-response-u

Example for calculating U value in DFT+U using CASTEP with the ab inito linear response method

Computing ab inito U value using the linear response method with CASTEP

How to run

1. Have CASTEP compiled and castep.mpi in the $PATH
2. base script.sh
3. Run this notebook or python post-process.py

How it works

Adjust the HUBBARD_ALPHA value and record the initial and final occupations of the Mn d levels when continuing from the unperturbed run (base_calc). The value of U is extracted using the gradient of the two response curves.

The example in http://hjkgrp.mit.edu/content/calculating-hubbard-u is reused here and the same methodology is followed.
The more self-consistent U can be computed by repeating the procedure with different input value for the U.

Reference:

Cococcioni, M.; de Gironcoli, S. Linear Response Approach to the Calculation of the Effective Interaction Parameters in the LDA+U Method. Phys. Rev. B 2005, 71 (3), 035105. https://doi.org/10.1103/PhysRevB.71.035105.

DISCLAIMER: Use at your own risk. Please raise an issue if you think the method here is not correct due to implementation details.