The separation and aggregation of Nb, Si, and N atoms around the NbN grain during the deposition of the Nb-Si-N nanocomposite film were discussed. The evolution behavior of the 2N2Nb island and the adsorption and diffusion energy of Nb, Si, and N atoms around the island on the NbN (0 0 1) surface were investigated using the first-principles method based on density functional theory. Results indicated that the most stable configuration of the Nb-Si-N island was the combination of Nb and N atoms to form the island and the possible aggregation of the Si atom to diagonal Nb atom outside the island. Substitution solid solution was eventually formed, in which the Nb atom of the 2N2Nb island was replaced by the Si atom during deposition. However, the Si atom was easily replaced by the Nb atom at the site with abundant Nb atoms. The diffusion energy of the evolution from Nb-2N1Nb1Si to Si-2N2Nb was 1.58 eV, and the total energy of the configuration decreased. Moreover, the interface of Si and NbN grains tended to separate. The highest energy adsorption sites for Nb, Si, N atoms adsorbed on the NbN (0 0 1) surface around the 2N2Nb island were P3, P1, and P2, respectively. The adsorption energies of Nb, Si, and N atoms on the NbN (0 0 1) surface around the 2N2Nb island were 7.3067, 5.3521, and 6.7113 eV, respectively, and their diffusion energies around the 2N2Nb island were 2.62, 1.35, and 5.094 eV, respectively. The low adsorption and diffusion energies of active Si atoms promoted the distribution of Nb and N atoms during deposition. Furthermore, the NbN grain was easily separated through Si atom diffusion into the 2N2Nb island. The grain was refined, and its growth was inhibited by the Si atom during deposition. (C) 2015 Elsevier B.V. All rights reserved.