A universal framework for multiconfigurational DFT

Prof. Mickaël Delcey Lund University, Lund, Sweden Abstract Strong correlation has been argued to be the last remaining weakness of DFT.[1] It shows up in several situations of high relevance to modern chemistry, such as transition metal complexes, especially antiferromagnetically coupled multi-metallic complexes, as well as in photochemistry, especially around conical intersections. Decades of development have provided us with a zoo of methods trying to solve this issue by combining DFT with multiconfigurational wavefunctions. This plethora of methods has dispersed the efforts of the community and prevented the emergence of a standard. Here, I show how most of these methods can be united under a single framework. Indeed, most of these approaches which are not already a form of multiconfigurational pair-density functional theory (MC-PDFT)[2] can benefit from being re-cast as one, simply becoming different MC-PDFT functionals. By implementing all these approaches into our recently introduced and highly efficient variational MC-PDFT implementation[3], we can for the first time compare them on a number of strong correlation cases. From these results and formal arguments, we provide useful insights for future functional developments. References: [1] A. D. Becke, J. Chem. Phys. 140, 18A301 (2014); N. Mardirossian and M. Head-Gordon, Mol. Phys., 115, 2315–2372 (2017) [2] F. Moscardó and E. San-Fabián, Phys. Rev. A, 44, 1549−1553 (1991); G. Li Manni, R. K. Carlson, S. Luo, D. Ma. J. Olsen, D. G. Truhlar and L. Gagliardi, J. Chem. Theory Comput., 10, 3669–3680. (2014) ​[3] M. Scott, G. L. S. Rodrigues, X. Li and M. G. Delcey, J. Chem. Theory Comput., 20, 2423–2432 (2024)