First Principles Electronic Structure Study of Ca₂CuO₂Cl₂

We discuss Density Functional Theory (DFT) based results on the oxychloride cuprate Ca₂CuO₂Cl₂ (CCOC), which are obtained by using the recently constructed Strongly-Constrained-and-Appropriately-Normed (SCAN) functional. Theoretical results are compared and contrasted with the corresponding angle-resolved photoemission (ARPES) measurements. Previous first-principles DFT studies have found the ground state of the half-filled CCOC to be metallic in sharp disagreement with the experimentally observed insulating state. Although the insulating behavior can be captured by introducing an empirical Hubbard U parameter in first-principles computations, that reduces the predictive power of the theory. In sharp contrast, the SCAN functional yields the antiferromagnetic insulator phase with a gap in good agreement with optical conductivity studies without the need to invoke the Hubbard U. We also discuss how the electronic structure of CCOC evolves with hole doping.