arXiv subjects

You-Zhao Lan

Publications and source records attributed to You-Zhao Lan.

7 recordsLinked to original sources

arXiv2023

Effects of opposite atoms on electronic structure and optical absorption of two-dimensional hexagonal boron nitride

We perform the first-principles many-body GW and Bethe-Salpeter equation (BSE) calculations on the two-dimensional hexagonal boron nitride (2D-hBN) to explore the effects of opposite atoms on the electronic structure and linear one-photon absorption (OPA). Five AA- and AB-stacked bilayer and eight AAB-stacked trilayer structures are considered. The AAB-stacked trilayer hBN (TL-BN) structures are constructed by mixing the AA- and AB-stacked bilayer hBN (BL-BN). We show that the GW approximation gives rise to different types (i.e., indirect or direct) of fundamental band gaps from the independent particle approximation for all structures except those dominated by the B-B opposite. The stacking modes dominated by the B-B opposite have a direct fundamental band gap in both approximations. The OPA spectra are calculated by solving the Bethe-Salpeter equation combined with the GW quasi-particle correction. Strong absorption peaks are found for most structures in the deep-ultraviolet region. The binding energy and Davydov splitting of excitons of TL-BN strongly depend on the opposite atoms and are related to the role of the stacking BL-BN substructure. Finally, taking the six-layer and below AB-stacked structures as examples, we show that the B-B opposite unit is helpful in constructing the turbostratic-phase-like stacking structures with a direct fundamental band gap which are more suitable for optoelectronic applications.

cond-mat.mtrl-sci↗

arXiv2021

Excitonic effects on the third-order nonlinear optical properties of solids: Theory and application

We present a many-body Bethe-Salpeter equation eigenstates based sum-over-states method to calculate the linear and nonlinear optical properties of solids. Excitonic and local field effects are included in the calculations. As applications, we calculate the one-photon absorption, third harmonic generation, degenerate four-wave mixing spectra of solid C60 fullerene. The overall agreement between the theoretical and experimental results is very good for all three calculated spectra. By comparisons with the independent particle approximation based sum-over-states method, we show that excitonic effects mix the independent particle transition peaks to new excitonic ones. The position and intensity of spectral peaks are modified significantly. By tracing the sum-over-states progress, we determine the type of nonlinear polarization resonances for the characteristic peaks of third harmonic generation process, which may clear up a discrepancy in two experimental results.

cond-mat.mtrl-sci↗

arXiv2020

Excitonic effect on two-photon absorption of two-dimensional semiconductors: Theory and applications to MoS2 and WS2 monolayers

Based on the Bethe-Salpeter equation eigenstates, we present a first-principles many-body formalism for calculating the two-photon absorption (TPA) coefficient of semiconductors. We apply this formalism to calculate the TPA spectra of MoS2 and WS2 monolayers. The all-electron full-potential linearised augmented-plane wave based functions are used for solving the Bethe-Salpeter equation. The calculated spectra are in good agreement with the available experimental ones for WS2 monolayer. The calculated TPA spectra exhibit significant excitonic effects when compared to those based on the independent particle approximation. The physical origin of TPA excitonic transitions of MoS2 and WS2 monolayers are revealed by tracing the sum-over-states process. We show that the spin-orbit coupling effect leads to characteristic double peaks with an interval of half spin-orbit splitting energy. These double peaks mainly originate from the transitions at the vicinity of K point.

cond-mat.mtrl-sci↗

arXiv2017

Origin of layer number dependent linear and nonlinear optical properties of two-dimensional graphene-like SiC

We theoretically discuss the physical origin of the dielectric constants [ε(ω)] and second harmonic generation coefficients [\{chi}(2)(ω)] of the ABA-stacked two-dimensional graphene-like silicon carbide (2D-SiC) with the number of layers up to 5. It is found that the intensities of the pronounced peaks of both ε(ω) and \{chi}(2)(ω) exhibit a clear layer number dependence. For the light polarization parallel to the 2DSiC plane, the monolayer SiC (ML-SiC) and multilayer SiC (MuL-SiC) have very similar pronounced peak positions of ε(ω), which are attributed to the π->π* and σ->σ* transitions. However, for the light polarization perpendicular to the 2D-SiC plane, a characteristic peak is found for the MuL-SiC at about 4.0 eV, except that the allowed π->σ* and σ->π* transition peaks are found for both ML-SiC and MuL-SiC in the high-energy region (> 8 eV). This characteristic peak is attributed to the interlayer π->π* transition which does not exist for the ML-SiC, and at this peak position, the ML-SiC has a weak dark exciton based on the mBJ calculation within the Bethe-Salpeter equation framework. For \{chi}(2)(ω), the single-particle transition channels based on the three-band terms dominate the second harmonic generation process of both ML-SiC and MuL-SiC and determine the size and sign of \{chi}(2)(ω). In the ultraviolet visible region, the purely interband motion and intraband motion of electrons competitively determine the size and sign of \{chi}(2)(ω). For the light polarization perpendicular to the 2D-SiC plane, the intraband motion of electrons modulated more dramatically the interband motion than for that parallel to the 2D-SiC plane.

physics.optics↗

arXiv2016

Full ab initio band structure analysis of interband and intraband contributions for third harmonic generation coefficient of bulk silicon: implementation and application of the sum-over-states

We fully implement the Aversa and Sipe sum-over-states formulism and make a full ab initio band structure analysis of interband and intraband contributions for the third-order nonlinear optical susceptibilities of bulk silicon. The band structure and momentum matrix elements were calculated by using the highly accurate all-electron full potential linearized augmented plane wave method within the local density approximation. The convergence tests including the scissor correction with different k-points meshes and empty states were performed. Both real and imaginary parts of susceptibility were directly calculated and checked by the Kramers-Kronig relation. The converged results are compared with other theoretical and experimental ones and in agreement with the recent ab initio real-time-based calculation. The nonlinear optical coefficient comes from three parts: the pure interband contribution (Pinter), the modulation of interband terms by intraband terms (Pmod), and the intraband contribution (Jintra). For each part, the origin of enhanced peaks is explored by tracing the sum-over-states process. The interband contribution is found to be dramatically modulated by the intraband contribution.

cond-mat.mtrl-sci↗

arXiv2014

Comprehensive understanding of size-, shape-, and composition-dependent polarizabilities of SimCn (m, n = 1-4) clusters

We theoretically investigate the size-, shape-, and composition-dependent polarizabilities of the SimCn (m, n = 1 - 4) clusters by using the density functional based coupled perturbed Hartree-Fock method. The size-dependence of the polarizabilities of the SimCn (m, n = 1 - 4) clusters is more complicated than that of pure Sim and Cn (m, n = 1 - 8) clusters because for a given cluster size the heteroatomic clusters have more isomers than the homoatomic ones. For the shape-dependence, we consider three kinds of shape, linear (chain), prolate, and compact. For most clusters, we can clearly observe orders of α(linear) > α(prolate) and α(prolate) > α(compact) for a given composition. The composition-dependence of polarizabilities reveals that the linear clusters have an obvious larger polarizability than both the prolate and the compact clusters especially for a given m/n value. The shape effect makes a main contribution to determine the size of the polarizability. To understand the size of polarizability and the evolution of polarizability, we have tried many factors, such as the energy gap and binding energy, and defined a new parameter (Δq) that characterizes the redistribution of charge in cluster. We find that both the binding energy and the Δq are more available than the energy gap for reflecting the evolution of polarizabilities provided that both the cluster shape and one of the components in cluster are fixed. The correlation between the polarizability and the energy gap is poor, in agreement with the previous results.

physics.atm-clus↗

arXiv2010

Dynamic second-order hyperpolarizabilities of Si2C and Si3C clusters using coupled cluster singles-and-doubles response approach

We investigate the dynamic second-order hyperpolarizabilities γ(-3ω; ω, ω, ω) (indicated by γTHG) of the Si2C and Si3C clusters using the highly accurate coupled cluster singles-and-doubles (CCSD) response approach. The static γ values of the Si2C and Si3C clusters are 1.99 \times 10-35 and 3.16 \times 10-35 esu, respectively. Similar to the α values, the γ values of the Si2C and Si3C clusters are smaller than those of the Si3 and Si4 clusters, respectively, which is related to much smaller static γ value of the C atom than the Si atom.

physics.atm-clus↗