In this study, the plasmon-enhanced high-order harmonic generation (HHG) of H-terminated finite-sized armchair single-walled carbon nanotubes (SWCNTs) near Ag nanoparticles is investigated systematically. Multiscale methods that combine the real-time time-dependent Hartree–Fock (TDHF) approach at the semi-empirical intermediate neglected differential overlap (INDOS) Hamiltonian level for molecular electronic dynamics with the finite-difference time-domain (FDTD) and solving Maxwell’s equations are used. It is found that for intact CNTs, HHG is significantly enhanced due to plasmon resonance. However, the nonlinear optical properties are saturated when the tube length increases enough in the inhomogeneous near-field. For long CNTs, the large gradient of a near-field is unfavorable for the nonlinear excitation of electrons. But defects can further change the properties of the spectra. The HHG of hybrid systems can be enhanced very clearly by introducing vacancy defects in CNTs. This enhancement is affected by the energy and intensity of the incident light, the near-field gradient, and the number and location of defects.

In this paper, the structural and electronic properties of P/SnBr₂ heterojunctions were investigated using the first-principles calculation method based on the density functional theory (DFT). The band alignment of the P/SnBr₂ heterojunction was type I. The bandgap value was 0.71 eV in the DFT calculation. Furthermore, the bandgap of the heterojunction could be efficiently tuned by controlling an electric field and biaxial strain. The bandgap changed linearly with the electric field in a certain range; when the electric field was greater than 0.8 V/Å, the heterojunction was metallic. The bandgap could also be tuned when a biaxial strain was applied. Under tensile or compressive stress, significant effects such as the band alignment shift from type I to type III, and the transition from indirect to direct bandgap occurred. In conclusion, these research findings provide theoretical guidance for designing new heterojunctions based on SnBr₂.