2012/06/30 by Christoph R. Jacob, Markus Reiher
Physics and Astronomy · #physics.chem-ph #cond-mat.other #quant-ph
paper · pdf · doi:10.1002/qua.24309
published as Int. J. Quantum Chem. 112, 3661-3684 (2012)
arxiv created 2012/10/25 · arxiv updated 2012/10/26
The accurate description of open-shell molecules, in particular of transition metal complexes and clusters, is still an important challenge for quantum chemistry. While density-functional theory (DFT) is widely applied in this area, the sometimes severe limitations of its currently available approximate realizations often preclude its application as a predictive theory. Here, we review the foundations of DFT applied to open-shell systems, both within the nonrelativistic and the relativistic framework. In particular, we provide an in-depth discussion of the exact theory, with a focus on the role of the spin density and possibilities for targeting specific spin states. It turns out that different options exist for setting up Kohn-Sham DFT schemes for open-shell systems, which imply different definitions of the exchange-correlation energy functional and lead to different exact conditions on this functional. Finally, we suggest some possible directions for future developments.