Fig. 1. Structure, reflectivity, and colour of LuH₂.

a Crystal structure of $Fm\overline{3}m$ LuH₂. b Reflectivity of LuH₂ calculated using semilocal density functional theory (DFT), DFT corrected with a Hubbard U term (DFT + U), and DFT including electron–phonon coupling (DFT + EPC). The experimental reflectivity is taken from ref. ¹⁵. c Colour and photorealistic rendering of LuH₂ calculated using DFT, DFT + U, and DFT + EPC. The photorealistic rendering is shown as LuH₂ surrounding a grey ball with an opening in the centre.