"ELF isosurface (isovalue of 0.75) plot for Sn16O32 (a) defect-free system and (b) supercell containing two oxygen vacancies. Red and blue colours stand for the regions of high and low localised electrons. Reproduced from ""The effect of oxygen vacancies on the hyperfine properties of metal-doped SnO2"", F H Aragón et al 2017 J. Phys. D: Appl. Phys. 50 115103. (C) IOP Publishing, all rights reserved."