  Sodium pentazolates NaN5 andNa2N5, new high energy density materials, are
discovered during first principles crystal structure search for the compounds
of varying amounts of elemental sodium and nitrogen. The pentazole anion N5- is
stabilized in the condensed phase by sodium Na+ cations at pressures exceeding
20 GPa, and becomes metastable upon release of pressure. The sodium azide
(NaN3) precursor is predicted to undergo a chemical transformation above 50 GPa
into sodium pentazolates NaN5 and Na2N5. The calculated Raman spectrum of NaN5
is in agreement with the experimental Raman spectrum of a previously
unidentified substance appearing upon compression and heating of NaN3.
