When combined X-ray and polarized neutron diffraction data challenge high-level calculations: spin-resolved electron density of an organic radical

Experimental joint refinement against X-ray and polarized neutron diffraction data has been performed to simultaneously model the charge and spin density of a free radical; the resulting model challenges density functional theory (DFT) calculations, but is in fair agreement with ab initio complete active-space self-consistent field (CASSCF) calculations.