Quantum Monte Carlo Study of the electronic properties of delafossite 2H-AgNiO₂ and AgNi_xCo_1-xO₂

 The delafossite AgNiO₂ has received a great deal of attention due to its unique semi-metallic nature, which only AgNiO₂ exhibits among the d¹⁰-based delafossites, and its antiferromagnetism in the NiO₂ layers. Due to the semi-metallic nature of AgNiO₂, the existence of a metal-insulator transition has been predicted in AgNi_xCo_1-xO₂ structures consisting of an admixture of insulating CoO₂ into the NiO₂. The electronic structure of AgNiO₂ have been studied using Density Functional Theory (DFT), but a detailed predictive study that includes accurate electron correlations in NiO₂ has been missing. Using Quantum Monte Carlo method, we obtain accurate estimates for the electronic properties of AgNiO₂. We also conclude that the rather strong electron correlations in AgNiO₂ were underestimated in DFT studies. Finally, we study various compositions of AgNi_xCo_1-xO₂ and estimate their formation energies and band gap openings with Co substitutions in order to investigate the electronic properties and phase stability of the mixtures.