Self-consistent calculation of Hubbard U parameters within linear-scaling DFT

DFT+U has proven to be a computationally efficient method for correcting for the underestimation of electron localization effects, or for the absent derivative discontinuity, inherent in conventional density functionals. Invoking an approximate interpretation of DFT+U as a corrective penalty functional for the spurious curvature of the total-energy with respect to subspace occupancy, the Hubbard U parameter may be calculated [1,2], in which case DFT+U may be considered to be fully first-principles approach. We describe our approach for computing the Hubbard U and Hund’s J parameters within ONETEP, a linear-scaling DFT code which comprises a complete DFT+U+J [3] implementation including ionic forces and a flexible choice of population analyses [4,5]. We discuss issues of charge preservation and self-consistency, and we demonstrate the capability of our method by means of numerical tests on the ground-state properties of selected molecules that present challenges for approximate DFT. [1] W. E. Pickett, et al., Phys. Rev. B, 58, 1201 (1998). [2] H. J. Kulik, et al., Phys. Rev. Lett. 97, 103001 (2006). [3] B. Himmetoglu, et al., Phys. Rev. B 84, 115108 (2011). [4] D. D. O’Regan, et al., Phys. Rev. B 85, 085107 (2012). [5] D. D. O’Regan, et al., Phys. Rev. B 83, 245124 (2011).