Minimum tracking linear response Hubbard and Hund corrected Density Functional Theory in CP2K

TL;DR

This paper introduces a new implementation of DFT+$U$+$J$ in CP2K, including a first-principles method for calculating $U$ and $J$ parameters, with benchmarking on various materials.

Contribution

The paper presents the first implementation of the minimum-tracking linear-response method for $U$ and $J$ in CP2K, along with analytical forces and comparisons of tensorial and L"owdin representations.

Findings

Consistent results with existing literature for band gaps and polaron stability.

Demonstrated the effectiveness of the linear-response method for $U$ and $J$ calculation.

Analyzed the impact of L"owdin orthonormalization on properties.

Abstract

We present the implementation of the Hubbard ($U$) and Hund ($J$) corrected Density Functional Theory (DFT+$U$+$J$) functionality in the Quickstep program, which is part of the CP2K suite. The tensorial and L\"owdin subspace representations are implemented and compared. Full analytical DFT+$U$+$J$ forces are implemented and benchmarked for the tensorial and L\"owdin representations. We also present the implementation of the recently proposed minimum-tracking linear-response method that enables the $U$ and $J$ parameters to be calculated on first principles basis without reference to the Kohn-Sham eigensystem. These implementations are benchmarked against recent results for different materials properties including DFT+$U$ band gap opening in NiO, the relative stability of various polaron distributions in TiO$_2$, the dependence of the calculated TiO$_2$ band gap on +$J$ corrections, and, finally, the role of the +$U$ and +$J$ corrections for the computed properties of a series of the hexahydrated transition metals. Our implementation provides results consistent with those already reported in the literature from comparable methods. We conclude the contribution with tests on the influence of the L\"owdin orthonormalization on the occupancies, calculated parameters, and derived properties.