Title: Multiconfigurational Short-Range Density-Functional Theory for Open-Shell Systems,
Abstract: Many chemical systems cannot be described by quantum chemistry methods based
on a singlereference wave function. Accurate predictions of energetic and
spectroscopic properties require a delicate balance between describing the most
important configurations (static correlation) and obtaining dynamical
correlation efficiently. The former is most naturally done through a
multiconfigurational (MC) wave function, whereas the latter can be done by,
e.g., perturbation theory. We have employed a different strategy, namely, a
hybrid between multiconfigurational wave functions and density-functional
theory (DFT) based on range separation. The method is denoted by MC short-range
(sr) DFT and is more efficient than perturbative approaches as it capitalizes
on the efficient treatment of the (short-range) dynamical correlation by DFT
approximations. In turn, the method also improves DFT with standard
approximations through the ability of multiconfigurational wave functions to
recover large parts of the static correlation. Until now, our implementation
was restricted to closed-shell systems, and to lift this restriction, we
present here the generalization of MC-srDFT to open-shell cases. The additional
terms required to treat open-shell systems are derived and implemented in the
DALTON program. This new method for open-shell systems is illustrated on
dioxygen and [Fe(H2O)6]3+.