Nitride has been drawing much attention due to its wide range of applications in optoelectronics and remains plenty of room for materials design and discovery. Here, a large set of nitrides have been designed, with their band gap and alignment being studied by first-principles calculations combined with machine learning. Band gap and band offset against wurtzite GaN accurately calculated by the combination of screened hybrid functional of HSE and DFT-PBE were used to train and test machine learning models. After comparison among different techniques of machine learning, when elemental properties are taken as features, support vector regression (SVR) with radial kernel performs best for predicting both band gap and band offset with prediction root mean square error (RMSE) of 0.298 eV and 0.183 eV, respectively. The former is within HSE calculation uncertainty and the latter is small enough to provide reliable predictions. Additionally, 2 when band gap calculated by DFT-PBE was added into the feature space, band gap prediction RMSE decreases to 0.099 eV. Through a feature engineering algorithm, elemental feature space based band gap prediction RMSE further drops by around 0.005 eV and the relative importance of elemental properties for band gap prediction was revealed. Finally, band gap and band offset of all designed nitrides were predicted and two trends were noticed that as the number of cation types increases, band gap tends to narrow down while band offset tends to go up. The predicted results will be a useful guidance for precise investigation on nitride engineering.

Applying an external electric field can induce a transition from a type-I to a type-II band alignment in an α-tellurene/MoS2 heterostructure.

Pressure has been demonstrated to be an effective parameter to alter the atomic and electronic structures of materials. By using the first-principles calculations based on density functional theory (DFT), we systematically investigated the changes in the atomic and electronic structures of the cubic MAPbI(3) phase under pressures. It is found that the band gap of the compressed cubic MAPbI(3) structure exhibits a remarkable redshift to 1.114/1.380 eV in DFT/HSE-SOC calculation under a mild pressure of 2.772 GPa, and subsequently shows a widening at higher pressures until similar to 20 GPa. As the pressure further increases, the band gap closes at similar to 80 GPa. Detailed structural and electronic characteristic analyses indicate that the band gap of the cubic MAPbI(3) structure is determined by two competing effects: the lattice contraction decreases its band gap while the PbI6 octahedral filling increases it. Given that, pressure can be a powerful tool to help understanding the optoelectronic properties of perovskite materials. AbstractPressure has been demonstrated to be an effective parameter to alter the atomic and electronic structures of materials. By using the first-principles calculations based on density functional theory (DFT), we systematically investigated the changes in the atomic and electronic structures of the cubic MAPbI3 phase under pressures. It is found that the band gap of the compressed cubic MAPbI3 structure exhibits a remarkable redshift to 1.114/1.380 eV in DFT/HSE-SOC calculation under a mild pressure of 2.772 GPa, and subsequently shows a widening at higher pressures until ∼20 GPa. As the pressure further increases, the band gap closes at ∼80 GPa. Detailed structural and electronic characteristic analyses indicate that the band gap of the cubic MAPbI3 structure is determined by two competing effects: the lattice contraction decreases its band gap while the PbI6 octahedral tilting increases it. Given that, pressure can be a powerful tool to help understanding the optoelectronic properties of perovskite materials.

Magnetized graphene is a promising candidate for spintronic devices, where half-semimetallic or -semiconducting property is highly desirable. Using first-principles calculations, we show that stable ferromagnetic ordering can exist readily in non-compensated bonding BN/graphene bilayer with triangular defects (TDs) by analogizing with bonding BN/BN bilayer observed in experiment. More intriguingly, regardless of the non-compensated defect states in the gap, such spin-polarized BN/graphene bilayer exhibits spin-gapless and -gapped semiconducting band structures with quadratic and linear dispersion, respectively, depending on the size of TDs. The massive or massless electronic states of bonding BN/graphene are associated with the electron localization degree at the zigzag edges of TDs. Our findings might provide another feasible strategy to realize stable magnetized graphene and engineer its electronic and magnetic features.

Practicability of CsSnI3 has been limited by the lack of stability in humid environment. Here we calculated phase stability, the impact of H2O embedded in CsSnI3 and surface adsorption by the first-principles calculations. Total energy results show that γ-CsSnI3 and Y-CsSnI3 are more stable. However, the γ-CsSnI3 is hydrophilic-like and Y-CsSnI3 is hydrophobic-like. γ-CsSnI3 studies show that H2O tend to adsorb at the hollow sites on the (001) surface. Strong coupling between O and Cs atoms and hydrogen bonding interactions between H and I atoms render the deformation of the (001) surface. These results are partially explained by the phase instability of perovskites in air.