Ice Carbons

On the basis of the topologically distinct oxygen nets of crystalline ice phases, a series of carbon structures with sp³ bonding are constructed. Five new low-energy polymorphous phases of carbon, named “ice carbons”, are predicted by using the first-principles calculations. Their hardnesses are about 88.5–98.5% that of diamond, indicating that these new carbon phases are superhard materials. In particular, the new “<i>ice</i>^III-carbon” has the highest hardness 94.1 GPa that only 1.4 GPa smaller than that of diamond. Moreover, it also has slightly lower bulk modulus, which display similar properties with <i>h</i>P3, <i>t</i>I12, and <i>t</i>P12 superdense carbon allotropes