Nature Reviews Materials 2, 17005 (2017)

References 11, 119, 170 and 177 were incorrect in this article. Reference 11 should be Mujica, A., Rubio, A., Muñoz, A. & Needs, R. J. High-pressure phases of group-IV, III–V, and II–VI compounds. Rev. Mod. Phys. 75, 863 (2003); reference 119 should be Hubert, H. et al. Icosahedral packing of B12 icosahedra in boron suboxide (B6O). Nature 391, 376–378 (1998); reference 170 should be Mao, W. L. et al. Hydrogen clusters in clathrate hydrate. Science 297, 2247–2249 (2002); and the year for reference 177 should be 2017. These have been corrected in both the HTML and PDF versions of the article.