Structures of 50 phosphorous-doped nitrogen clusters (NnPm, n + m = 4, 8, 10, 14, 16, 20) were optimized employing M062X/6-311++G(d,p) and B3LYP/6-311++G(2df,p) methods. The Delta G and Delta H values of formation of the clusters from nitrogen and phosphorous atoms as well as binding energies per atom (E-b) of the clusters were computed. The calculations showed that the NnPm clusters are more stable than pure Nn+m or Pn+m clusters. For instance, the E-b of N4P6 (3.48 eV) was about 50% larger than that for N-10 (2.49 eV) and P10 (2.34 eV) clusters. (C) 2016 Elsevier B.V. All rights reserved.