The structural stability of K-4 nitrogen was studied by performing first-principles calculations. The total energy as a function of isotropic deformations and volume-conserving tetragonal and trigonal deformations was calculated. The total energy was a minimum under all three deformations, suggesting that K-4 nitrogen is a mechanically stable phase. However, the results of phonon dispersion calculations indicated that it is dynamically unstable. Our results also indicated that structural stability can be maintained by doping the K-4 nitrogen lattice with carbon, and that the resulting material will be a promising candidate as a high energy density material. (c) 2011 Elsevier B.V. All rights reserved.