Constructing two-dimensional (2D) van der Waals (vdW) heterostructures is a promising strategy to improve the photocatalytic efficiency of a single 2D material and has attracted wide attention. Here, the electronic structures, optical properties, and photocatalytic mechanism of the 2D GeC/BSe vdW heterostructure are investigated by first-principles calculations. It is demonstrated that the GeC/BSe heterostructure is comparatively very stable and possesses a staggered band alignment configuration. An intrinsic built-in electric field from the GeC layer to the BSe layer would be established at the interface, allowing the formation of Z-scheme charge transfer mode in the GeC/BSe heterostructure. Furthermore, its band edges exactly straddle the water redox potentials; overall water splitting can thus be expected. The GeC/BSe heterostructure also has a good light absorption coefficient with the magnitude order of ${10}^5\mathrm{c}{\mathrm{m}}^{-1}$. Moreover, it is proposed that the adoption of tensile strain can further promote the optical absorptions in the visible light range because of the favorable modulation in the bandgap, which benefits the photocatalytic reaction. Finally, the excellent abilities of ${\mathrm{H}}_2\mathrm{O}$ adsorption and ${\mathrm{H}}_2$ desorption are shown in the GeC/BSe heterostructure. These features make the GeC/BSe heterostructure promising for application in photocatalysis for water splitting.

Recently developed halide double perovskites $A_2{M}^{+}{M}^{3+}{X}_6$ have attracted attention as potential lead-free perovskite solar cell absorbers. Here, the stability, electronic, and optical properties of the lead-free inorganic-organic hybrid double perovskites ${\left({\mathrm{CH}}_3{\mathrm{NH}}_3\right)}_2\mathrm{InBi}{X}_6$ ($X$ = halogen) are studied based on density functional theory. By investigating the thermodynamic stability against decomposition, the ${\left({\mathrm{CH}}_3{\mathrm{NH}}_3\right)}_2\mathrm{InBi}{X}_6$ double perovskites are shown to be stable. Furthermore, the use of a small magnitude of hydrostatic pressure is proposed to improve the thermodynamic stability of double perovskites ${\left({\mathrm{CH}}_3{\mathrm{NH}}_3\right)}_2\mathrm{InBi}{X}_6$. Meanwhile, the calculated electronic band structures of ${\left({\mathrm{CH}}_3{\mathrm{NH}}_3\right)}_2\mathrm{InBi}{X}_6$ double perovskites exhibit suitable direct band gaps, small carrier effective masses, and three-dimensional electronic dimensionality. This, in turn, leads to strong optical absorption. Both the electronic and optical features make double perovskites ${\left({\mathrm{CH}}_3{\mathrm{NH}}_3\right)}_2\mathrm{InBi}{X}_6$ suitable for applications in optoelectronics.

In this theoretical study, a photonic crystal coupled-cavity waveguide created on polymer substrate was demonstrated to provide high-performance slow light with low group-velocity dispersion and large normalized delay–bandwidth product. Combined with structural-parameter optimization, the normalized delay–bandwidth product was enhanced to a large value of 0.809, and the group-velocity dispersion was on the order of 10 4 ( p s 2 / k m ) . Furthermore, the optimized coupled-cavity waveguide had tunability capabilities by changing the external pump laser power. Importantly, while adjusting the slow light, the normalized delay–bandwidth product values remained above 0.8, which was necessary to maintain the performance of optical buffering devices.

Solid-state high-order harmonic generation (HHG) now is a strong tool for detecting target properties, like band structure, Berry curvature and transition dipole moments (TDMs). However, the physical mechanism of high-order harmonic generation (HHG) in solids has not been fully elucidated. According to previously published works, in addition to the inter-band polarization, intra-band currents, and anomalous currents due to Berry curvature, there is another term which will be called the mixture term (MT). Taking monolayer ZnO as a sample, it is found that the intensity of the mixture term, which has been ignored for a long time in previous works, actually is comparable with other terms. Additionally, we compare the orientation-dependent HHG spectra that originated from different mechanisms. It is found that the inter-band and mixture HHG show similar orientation features. Meanwhile, Berry curvature only produces perpendicularly polarized even harmonics, and intra-band perpendicularly polarized even harmonics show special orientation features which can be explained by the orientation-dependent group velocity. This work will help people understand the mechanisms of solid-HHG better.

Porous nanocarbon materials are seen as potential excellent materials for hydrogen storage due to their high surface area, excellent cycling stability and favorable kinetics. This study employs Density Functional Theory (DFT) simulations to investigate key property of Li$^-$ and Na$^-$ modified PHE-graphene, including structural stability, electronic properties, and hydrogen storage capabilities. The results show that when each Li atom adsorbs six hydrogen molecules, the material reaches the maximum hydrogen adsorption gravimetric density of 15.20 wt%. Additionally, through Grand Canonical Monte Carlo (GCMC) simulations, we obtained the hydrogen weight ratios and adsorption enthalpy curves for Li- and Na-modified PHE under varying temperature and pressure conditions. These findings indicate that both Li- and Na-modified PHE-graphene are exceptional candidates for hydrogen storage materials, particularly in mobile applications.