High-order harmonic generation (HHG) in imperfect lattices with point defect vacancies is studied using a self-consistent time-dependent density-functional approach for a one-dimensional linear chain with a band gap. Compared with a perfect lattice with no vacancies, the HHG yield decreases by increasing the number of evenly distributed vacancies but remains almost unchanged in the case when vacancies are localized at neighboring lattice points. By introducing atomic-type point vacancies in the linear chain, it is effectively partitioned into several subsystems and the overall shape of HHG spectra of the resulting system can be modeled via the HHG of its subsystems provided each subsystem is large enough to behave like a bulk solid. For sufficiently small subsystems, the HHG spectra show detectable signatures of finite structure but maintains the overall structure of the spectrum of a bulk solids. A time-frequency profile of the emitted harmonics shows less regular sinusoidal patterns in the systems with vacancies compared with the perfect lattice. The role the vacancy-induced defectstate orbitals in the HHG process is investigated for different realizations of the linear chain and laser parameters.

The electronic properties, adsorption energies and energy barrier of sodium ion diffusion in B-doped graphyne (BGY) are studied by density functional theory (DFT) method.

We study the crystal-momentum-resolved contributions to the high-order harmonic generation (HHG) in band-gap materials, and identify the relevant initial crystal momenta for the first and higher plateaus of the HHG spectra. We do so by using a time-dependent density-functional theory model of one-dimensional linear chains. We introduce a self-consistent periodic treatment for the infinitely extended limit of the linear chain model, which provides a convenient way to simulate and discuss the HHG from a perfect crystal beyond the single-active-electron approximation. The multiplateau spectral feature is elucidated by a semiclassical k-space trajectory analysis with multiple conduction bands taken into account. In the considered laser-interaction regime, the multiple plateaus beyond the first cutoff are found to stem mainly from electrons with initial crystal momenta away from the point (k = 0), while electrons with initial crystal momenta located around the point are responsible for the harmonics in the first plateau. We also show that similar findings can be obtained from calculations using a sufficiently large finite model, which proves to mimic the corresponding infinite periodic limit in terms of the band structures and the HHG spectra.