Using theoretical methods, an international group of scientists led by Artem R. Oganov, Professor of Skoltech, Stony Brook University and Moscow Institute of Physics and Technology predicted unusual nitrides of hafnium and chromium with the chemical formulae HfN10 (and its zirconium analogue ZrN10) and CrN4. These compounds can be obtained at relatively low pressures and contain high-energy groups of nitrogen atoms. Pure polymeric nitrogen is an ideal high-energy compound that packs so much energy per unit volume or mass that it could be used as a powerful explosive if it were not for the gigantic pressures required for its synthesis. This work shows that nitrogen polymerizes at much lower pressures in the presence of metal ions. The authors also predicted a range of new hafnium nitrides as well as nitrides, carbides and borides of chromium, with an unusual combination of properties (high hardness, electrical conductivity, and toughness).