Multiconfigurational Short-Range Density-Functional Theory for Open-Shell Systems

TL;DR

This paper extends the multiconfigurational short-range density-functional theory (MC-srDFT) to open-shell systems, enabling accurate and efficient treatment of complex chemical systems with static and dynamic correlation, demonstrated on dioxygen and a ferric complex.

Contribution

The authors generalize MC-srDFT to open-shell systems by deriving and implementing necessary additional terms, broadening its applicability to more complex chemical systems.

Findings

Successfully applied to dioxygen and [Fe(H2O)6]3+

Improves treatment of static and dynamic correlation

Enhances efficiency over perturbative methods

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+.