Delocalization Error in DFT-Predicted Extreme Long-Range Functionalization of Carbon-Doped Hexagonal Boron Nitride

Abstract

Delocalization error is a serious failure of approximate density functional theory (DFT). This work shows how delocalization error affects the predicted catalytic activity of carbon-doped hexagonal boron nitride. While the charge and spin of an isolated carbon dopant are themselves predicted to be localized, nonhybrid DFT approximations predict spurious long-range transfer of charge and spin from such dopants to distant hydrogen adatom and molecular oxygen adsorbates. This effect mirrors nonhybrid DFT approximations’ predicted spurious long-range charge transfer in other systems, for example, dissociated heteronuclear diatomics Liᵟ⁺–Fᵟ⁻. The effect is robust to simulation details, occurring in finite-cluster, one-dimensionally periodic, and plane-wave periodic supercell simulations. In extreme cases, a single carbon dopant is predicted to activate molecular oxygen adsorbed 50 nm away and activate an isolated O₂ molecule suspended 1 μm away. The effect is traced to nonhybrid approximations’ delocalization error, which produces incorrect convex curves of energy as a function of fractional charge transfer from the carbon dopant to molecular oxygen. Long-range-corrected hybrid DFT approximations mitigate these delocalization errors and predict that carbon dopants will only activate adjacent molecular oxygen. This motivates adoption of long-range-corrected hybrids in future DFT simulations of doped boron-nitride nanostructures.