The state-of-the-art all-electron FLPAW method and the BoltzTrap software package based on semi-classical theory were adopted to explore the electronic structure and the optical and thermoelectric properties of Ga1-xInxN. Ga1-xInxN is predicted to be a direct band gap material for all values of x. Moreover, the band gap varies between 2.99 eV and 1.95 eV as x changes. Optical parameters such as the dielectric constant, absorption coefficient, reflectivity and refractive index are calculated and discussed in detail. The doping of In plays an important role in the modulation of the optical constants. The static dielectric constant epsilon(0) of Ga1-xInxN was calculated as 3.95, 3.99, 3.99 and 4.03 at x = 0.00, 0.25, 0.50 and 0.75, respectively. The static refractive index is 2.0 for pure Ga1-xInxN at x = 0.00. The thermal properties varied greatly as x fluctuated. The ternary alloy has large values for the Seebeck coefficient and figure of merit at high temperatures and is thus suitable for thermoelectric applications. Pure Ga1-xInxN at x = 0 exhibited ZT = 0.80 at room temperature, and at higher temperatures, the thermal conductivity decreased with increased In doping. (C) 2015 Elsevier B.V. All rights reserved.