Performance of the r<sup>2</sup>SCAN Functional in Transition Metal Oxides
S. Swathilakshmi, Reshma Devi, Gopalakrishnan Sai Gautam
Abstract
We assess the accuracy and computational efficiency of the recently developed meta-generalized gradient approximation (metaGGA) functional, restored regularized strongly constrained and appropriately normed (r 2 SCAN), in transition metal oxide (TMO) systems and compare its performance against SCAN. Specifically, we benchmark the r 2 SCAN-calculated oxidation enthalpies, lattice parameters, on-site magnetic moments, and band gaps of binary 3 d TMOs against the SCAN-calculated and experimental values. Additionally, we evaluate the optimal Hubbard U correction required for each transition metal (TM) to improve the accuracy of the r 2 SCAN functional, based on experimental oxidation enthalpies, and verify the transferability of the U values by comparing against experimental properties on other TM-containing oxides. Notably, including the U -correction with r 2 SCAN increases the lattice parameters, on-site magnetic moments, and band gaps of TMOs, apart from an improved description of the ground state electronic state in narrow band gap TMOs. The r 2 SCAN and r 2 SCAN+ U calculated oxidation enthalpies follow the qualitative trends of SCAN and SCAN+ U, with r 2 SCAN and r 2 SCAN+ U predicting marginally larger lattice parameters, smaller magnetic moments, and lower band gaps compared to SCAN and SCAN+ U, respectively. We observe the overall computational time (i.e., for all ionic+electronic steps) required for r 2 SCAN(+ U ) to be lower than SCAN(+ U ). Thus, the r 2 SCAN(+ U ) framework can offer a reasonably accurate description of the ground state properties of TMOs with better computational efficiency than SCAN(+ U ).