Standard density functional theory (DFT) methods used in condensed matter physics, including the local density approximation (LDA) and generalized gradient approximation (GGA), are known to fail in treating transition-metal compounds properly. To describe the localized electrons in this class of materials more accurately, an additional corrective term similar to the U term in the Hubbard model is added to standard DFT functionals. This method, known as DFT+ U , has been widely used since its introduction in 1991 by Anisimov, Zaanen, and Andersen. The U parameter in DFT+ U depends on the on-site Coulomb interaction between the localized electrons; therefore, it should be determined from the first principles rather than treated as a fitting parameter. A linear-response approach to determine the Hubbard U was introduced in 2005 [1]. This scheme has been implemented in Quantum Espresso (QE) [2], a DFT-calculation code adopting the plane-wave pseudopotential method. For many cases, the Hubbard U needs to be determined in a self-consistent manner, known as self-consistent U ( U sc ) [3-5].

In this study-group meeting, we have invited Dr. Han Hsu of National Central University to give a tutorial lecture on the computation of U sc . The meeting is scheduled to begin with the lecture regarding the implementation of DFT+ U sc in QE, followed by a hands-on session. For potential participants, installation of QE on their own machines is highly recommended. Some relevant references are listed below, and more will be announced later.

[1] M. Cococcioni and S. de Gironcoli, Phys. Rev. B 71 , 035105 (2005) and references therein.

[2] P. Giannozzi et al., J. Phys: Condens. Matter 21 , 395502 (2009).

[3] H. J. Kulik, M. Cococcioni, D. A. Scherlis, and N. Marzari, Phys. Rev. Lett. 97 , 103001 (2006).

[4] V. L. Campo Jr. and M. Cococcioni, J. Phys.: Condens. Matter 22 , 055602 (2010).

[5] H. Hsu, P. Blaha, M. Cococcioni, and R. M. Wentzcovitch, Phys. Rev. Lett. 106 , 118501 (2011).