A Consistent, Linear-Response Approach to LDA+U

Wednesday, August 1, 2007 - 3:00pm - 4:00pm
EE/CS 3-180
Matteo Cococcioni (University of Minnesota, Twin Cities)
Hubbard U-corrected DFT functionals have been very successful in describing several strongly-correlated
systems for which standard approximations to DFT fail. Unfortunately no explicit expression exists for the
effective electronic interaction parameter (the Hubbard U) contained in the corrective (+U) functional
and semiempirical estimates have been often used to determine its value. In this talk, after a general introduction
to the LDA+U method, I will present our linear response approach to the evaluation of the Hubbard U [1].
Within this approach the on-site electronic coupling is computed from the response of the considered system
to a shift in the potential acting on its correlated atomic states. Specifically, it is evaluated as the difference between
the inverse of the bare and fully interacting response matrices. The U we obtain thus corresponds to the effective
(atomically averaged) interaction between electrons that are located on the same site.

In this way the strength of the +U correction is consistently evaluated from the same DFT scheme we aim to correct;
the LDA+U is transformed in a completely ab-initio method with no need for any empirical evaluation of the effective coupling.
The results are also largely independent on the choice of the localized orbitals: the same occupation matrix that enters
the expression of the +U correction is consistently used to compute the effective interaction parameter.

With this approach we successfully studied the structural, electronic, chemical and electrochemical properties of several
transition metals compounds. Examples of applications will include minerals in the Earth's interior [1], cathode materials
for next-generation lithium-ion batteries [2] and catalysis reactions on molecules [3].

[1] M. Cococcioni and S. de Gironcoli, PRB (2005).

[2] F. Zhou, M. Cococcioni, A. C. Marianetti, D. Morgan and G. Ceder, PRB (2004).

[3] H. J. Kulik, M. Cococcioni, D. Scherlis and N. Marzari, PRL (2007).