Origin of f-orbital-bonding insensitivity to spin-orbit coupling in UO2

The origin of negligible spin-orbit coupling effects on the ground-state properties of UO2 is examined using the LDA+DMFT and the LSDA+U methods. Although the previous theoretical results neglecting the spin-orbit coupling (SOC) are in reasonable agreement with experiments, this insensitivity has not been investigated. Via the charge density distribution, we show that the SOC does not affect the U-O bonding states which are directly related to the bonding properties (e.g., lattice constant, bulk modulus, and oxidation/reduction energies).