Assessment of SCAN and regularized SCAN functionals with and without self-interaction correction

The Strongly Constrained and Appropriately Normed (SCAN) functional is a non-empirical meta-GGA functional that satisfies all the known 17 exact constraints that a meta-GGA functional can. Its numerical implementation is challenging and its use requires extremely fine numerical grids. The numerical issues become even more pronounced for the Perdew-Zunger (PZ) self-interaction correction (SIC) method as it requires evaluating the functional and its derivatives with orbital density that varies rapidly compared to total density. Bartok and Yates recently proposed a modification to SCAN, called regularized SCAN (rSCAN) to remove some of the numerical instabilities of SCAN. We have implemented rSCAN functional in our Fermi-Lowdin Self-Interaction Correction code and performed assessment of rSCAN for various molecular properties using standard datasets. We find rSCAN gives similar results to SCAN despite violation of some of the constraints and requires comparatively coarser grids than SCAN. However, like SCAN, rSCAN also shows numerical instabilities in PZ-SIC calculations where orbital densities are used. This problem is due to the use of variable α in these functionals. A solution to this numerical instability is suggested and implemented.