The photocatalytic, transport, photophysical, and structural properties of Tl10Hg3Cl16 single crystals are investigated by means of density functional theory in order to investigate its suitability to be used as an active photocatalyst. The calculation show that this compound possesses a narrow direct band gap. The obtained values of the fundamental energy band gap are about 0.82 eV (LDA), 0.88 eV (PBE-GGA), and 0.97 eV (mBJ). The absorption edge of Tl10Hg3Cl16 occurs at lambda = 742.3 nm, and the optical band gap is estimated to be 1.67 eV. For use in photocatalytic water splitting, the optical band gap of the photocatalyst material must be sufficiently large to overcome the endothermic character of the water-splitting reaction, i.e., higher than 1.23 eV therefore, Tl10Hg3Cl16 (Eg = 1.67 eV) is expected to be an active photo catalyst. The calculated density of states reveals the orbitals that form the conduction band minimum and the valence band maximum, and the existence of hybridization. The transport properties are calculated to investigate the suitability of Tl10Hg3Cl16 as a thermoelectric power generator, as an active photocatalyst for clean energy resources, and as an ultrafast scintillator for medical imaging. (C) 2017 Elsevier Inc. All rights reserved.