  The temperature dependence of the optical and magnetic properties of CuO were
examined by means of hybrid density functional theory calculations. Our work
shows that the spin exchange interactions in CuO are neither fully
one-dimensional nor fully three-dimensional. The large temperature dependence
of the optical band gap and the 63Cu nuclear quadrupole resonance frequency of
CuO originate from the combined effect of a strong coupling between the spin
order and the electronic structure and the progressive appearance of
short-range order with temperature.
