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Two - dimensional materials become one of the research hotspots due to the excellent optical, mechanical, thermal and magnetic properties. SnO2 film is a kind of excellent semiconductor material with high electron mobility, good conductivity and transparency. In this paper, the electronic structures, electronic state densities, electrical conductivities and optical properties of pure and doped SnO2 have been studied using the first principles of density functional theory. The calculation results show that a lot of impurity levels are generated near the Fermi level of two - dimensional SnO2 compared with three - dimensional SnO2, which improves the carrier concentration, reduces the band gap, enhances the localization of electrons, increases the effective mass of electrons in the conduction band, and facilitates the occurrence of electronic transitions, thus increasing the conductivity of materials. Two - dimensional SnO2 material has stronger electrical polarization ability than three - dimensional SnO2 material, and has better photon absorption performance and higher photoconductivity in infrared, visible and ultraviolet regions, which is more favorable for the separation and migration of photoelectron - hole pairs, that is, it can effectively improves its photoelectric conversion efficiency. Secondly, doping La can better improve the ability of absorbing photons in infrared, visible and ultraviolet regions, which is more conducive to the efficiency of photoelectric conversion and improve the conductivity. [ABSTRACT FROM AUTHOR]

Based on the plane waveultra soft pseudopotential method of density functional theory (DFT), the electronic structures and optical properties of intrinsic AIN, CAIN, Na - AIN and C-Na- AIN were calculated. It is concluded that after doping, lattice distortion occurs in each system compared with intrinsic AIN, and the binding energy of C - Na-AIN system is the smallest and the system is the most stable. Compared with the intrinsic AIN, the band gap width of the doped system decreases to varying degrees, resulting in an increase in the probability of electron transition in the system, especially in the C-Na- AIN system, which requires less energy for electron transition. After doping, the absorption band edge has a red shift, which widens the response range of AIN system to light and enhances the light absorption. Moreover, C-Na- AIN system has the strongest light absorption ability in the visible light region. From the analysis of dielectric function diagram, it can be seen that C-Na-AIN system has the largest dielectric constant, indicating that its charge binding ability is the strongest, the stability of the system is strong, and the polarization ability is the best. [ABSTRACT FROM AUTHOR]

Based on the first principle method of density functional theory, this paper studies the stabilities, electronic structures, and optical properties of Sc, C single doped and co-doped MgS systems. The results show that compared with the intrinsic MgS system, the binding energy of the doped system is still negative, indicating that the doped systems are in a stable state. Among them, the binding energy of Sc-C co-doped MgS system is the smallest, indicating that Sc-C co-doped system is the most stable. After doping, the band gap width of the system decreases, indicating that the energy of electron transition from valence band to conduction band decreases. In addition, the doping system has an obvious red shift in the low-energy region, indicating that Sc and C doping can effectively broaden the response range of the system to visible light. Among them, Sc-C-MgS system produces impurity levels near the Fermi level, and the band gap width is small. The absorption coefficient is the best in the visible light range. It can be inferred that Sc-C co-doping can be used as an effective means to improve the photocatalytic activity of MgS system. [ABSTRACT FROM AUTHOR]

In this paper, the electronic structure and magnetic properties of SnO2 doped with non-metallic elements (N) and transition metal elements (Mo, Ru, Rh, Pd) are calculated and analyzed based on the first principles approach. The results show that: the formation energy is closely related to the transition metal atomic radius, with the increase of the transition metal atomic radius, the formation energy is decreasing, where the N-Mo doping system has the lowest formation energy, so the system is the easiest to doping formation; energy band structure analysis shows that due to the number and distribution of spin up/spin down impurity energy levels of the doping system are asymmetric, the doping systems are magnetic generation; further exploration of the density of states shows that The magnetic properties of the doped system are due to the p-d orbital hybridisation between the transition metal atoms and the N atoms, the vacancies in the outermost electron orbitals and the single electron coupling. The results show that the SnO2 system is magnetic due to the introduction of doping atoms, and the doped system exhibits subferromagnetic properties, with the best magnetic moment of 1.88 μB for the N-Rh doped system, which is expected to be a good dilute magnetic semiconductor material. [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]

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]