We carry out ab initio electronic structure calculations of (SixSn1 (-) (x))(3)N-4 using density functional theory with projector augmented-wave potentials under the generalized gradient approximation. We find that the energetically favorable structure of Sn3N4 is the face-centered cubic spinel structure, followed by the hexagonal structure which has energy band gaps of 1.85 eV and 1.44 eV respectively. The (SixSn(1 - x))(3)N-4 ternary compound can exhibit both cubic and hexagonal crystal structures over the full range of x. However, the cubic structure is found to be energetically favorable for x < 0.3 above which the hexagonal structure of (SixSn(1 - x))(3)N-4 dominates. The energy band gap can be tuned continuously from 1.44 eV up to 5.8 eV in the case of the hexagonal crystal structure of (SixSn(1 - x))(3)N-4 and from 1.85 eV to 4.82 eV in the case of cubic (SixSn(1 - x))(3)N-4. Nevertheless the energy gap of (SixSn(1 - x))(3)N-4 is direct only for x < 0.3 when it is cubic and for x < 0.5 when hexagonal. (C) 2015 Elsevier B.V. All rights reserved.