DC24: A New Density Coherence Functional for Multiconfiguration Density-Coherence Functional Theory

In this study, we explored several alternative functional forms to construct more accurate and more physical density coherence functionals for multiconfiguration density-coherence functional theory. Each functional is parameterized against the same database as used in our previous work. The best density coherence functional, which is called DC24, has a more physical interpretation, and – as a side benefit – it also has a mean unsigned error of 1.73 kcal/mol, which is a 9% improvement as compared to the previous functional. The article also contains a new definition of the unpaired electron density, which may be useful in other contexts as well.