From these results, the novel stable and cohesive tet-C 4 is confirmed as the simplest dense carbon allotrope very close to diamond. Such elementary configuration can also serve as a "seed" template structure to generate large cells for the search of novel ultra-hard phases , as well as to model physical properties of diamond modified by doping for instance . [23] 2.5221 [23] 4.1186 [23] 3.516 97 443