Fig. 3: Highly symmetric high-Tc systems.

This figure shows five compounds related to the Tc spike around a hydrogen–hydrogen distance of 1.55 Å. The pink spheres refer to hydrogen atoms, while the rest refer to the respective host atoms. An ELF isosurface is depicted in each case. Also the shortest H–H (DHH) and H–X (DHX) distances are noted. Most of these compounds belong to the covalent family and show a purple ELF isosurface. The Si2H6 compound is an electride (note the small ELF bubbles in empty sites) and its ELF isosurface is shown in orange.