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The stability, electronic structures, work function, and optical properties of single-layer g-C3N4 and X/ g-C3N4 (X = g-C3 N4 , AlN and GaN) heterostructures were investigated using plane-wave density functional theory with ultra-soft pseudopotentials. The results show that the lattice mismatch ratio and lattice mismatch energy of X/ g-C3N4 heterojunction are very low, indicating that X/ g-C3N4 heterojunction has excellent stability. Compared with the single-layer g-C3N4, the bandgap of the X/ g-C3N4 all reduces, and the peaks and troughs of the density of states greatly improves. At the same time, X/ g-C3N4 has a redshift, which leds to an increase in the number of electrons in the excited state, making electronic transitions easier. It shows that the heterojunction is beneficial to improves the response-ability of the system to visible light, and effectively improves the photocatalytic activity of the system. Further calculations show that the work function of X/ g-C3N4 reduces and a built-in electric field is formed at the interface, which inhibits the recombination of photo-generated electron-hole pairs. This is of great benefit to the migration of carriers and the improvement of photocatalytic ability. Among them, the GaN/ g-C3 N4 heterojunction has the smallest work function, the potential difference at the interface formed a built-in electric field and the redshift is the most obvious. It can be inferred that the GaN/ g-C3 N4 heterojunction has the best photocatalytic activity. Therefore, the heterojunction proposed in this paper is an effective means to improve the photocatalytic activity of the system. [ABSTRACT FROM AUTHOR]

The electronic structure, magnetic properties and optical properties of anatase TiO2 and Cr doped anatase TiO2 ( 1/8, 1/16, 1/32) were studied by first principles GGA + U method. The calculation results show that the binding energy of Ti 0. 9375 Cr0. 0625 O2 is the smallest in all doping systems. Therefore, the stability of Ti 0. 9375 Cr0. 0625 O2 system is higher than that of Ti0. 875 Cr0. 125 O2 and Ti0. 96875 Cr0. 03125 O2, the doping of Cr leads to lattice distortion, which is beneficial to the separation of photogenerated holes and electron pairs, and improves the photocatalytic performance. At the same time, because of the interaction of Cr - 3d and 0 - 2p electrons, the doped system presents ferromagnetic properties, and with the increase of doping concentration, the system will have better ferromagnetic properties. Compared with the intrinsic TiO2, the absorption band edge of the doped system is red shifted and the spectral response range is enlarged, Moreover, with the increase of doping concentration, the light response range also increases, which effectively enhances the absorption ability of the system for visible light. [ABSTRACT FROM AUTHOR]