Charge density and redox potential of linio₂ using ab initio diffusion quantum monte carlo

We investigate the charge densities, lithium intercalation potentials, and Li-diffusion barrier energies of Li_xNiO₂ (0.0 < x < 1.0) system using the diffusion quantum Monte Carlo (DMC) method. We find an average redox potential of 4.1(2) eV and a Li-diffusion barrier energy of 0.39(3) eV with DMC. Comparisoin of the charge densities from DMC and density functional theory (DFT) and show that local and semilocal DFT functionals yield spin polarization densities with an incorrect sign on the oxygen atoms. The SCAN functional and Hubbard-U correction improves the polarization density around Ni and O atoms, resulting in smaller deviations from the DMC densities. DMC accurately captures the many-body nature of Ni-O bonding, hence yielding accurate lithium intercalation voltages, polarization densities, and reaction barriers.