Y.-Z. Lan

A theoretical investigation of hyperpolarizability for small GanAsm (n+m=4–10) clusters

In this paper, the second and third order polarizabilities of small Ga(n)As(m) (n + m=4-10) clusters are systematically investigated using the time dependent density functional theory (TDDFT)6-311+G* combined with the sum-over-states method (SOSTDDFT6-311+G*). For the static second order polarizabilities, the two-level term (beta(vec.2)) makes a significant contribution to the beta(vec) for all considered Ga(n)As(m) clusters except for the Ga3As4 cluster. And, for the static third order polarizabilities, the positive channel (gamma(II)) makes a larger contribution to gamma(tot) than the negative channel (gamma(I)). Similar to the cubic GaAs bulk materials, the small Ga(n)As(m) cluster assembled materials exhibit large second order (1 x 10(-6) esu) and third order susceptibilities (5 x 10(-11) esu). The dynamic behavior of beta(-2omega; omega, omega) and gamma(-3omega; omega, omega, omega) show that the small Ga(n)As(m) cluster will be a good candidate of nonlinear optical materials due to the avoidance of linear resonance photoabsorption.

TDHF-SOS treatments on linear and nonlinear optical properties of III-V semiconductor clusters (Ga3As3, Ga3Sb3, In3P3, In3As3, In3Sb3)

Abstract We employ an ab initio time-dependent Hartree–Fock (TDHF) formalism combined with sum-over-states (SOS) method to calculate the linear and nonlinear optical properties of direct semiconductor clusters. The obtained electronic absorption spectra predict a variety of the spectral shapes and peak positions and an increase of the second-order nonlinear optical response with an increase of V-group ionic radius in the title clusters. Charge transfers from the π bonding to π antibonding orbitals between III and V group atoms make a significant contribution to the second-order polarizability.

First-principles calculations of band structures and dynamic optical properties of CsCdBr3 and RbCdI3∙H2O crystals

We report the band structures as well as frequency-dependent (dynamic) linear and nonlinear optical properties of CsCdBr3 and RbCdI3∙H2O crystals calculated within density functional theory with a nonlocal gradient correction, including the dielectric function, linear and nonlinear refractive indices, frequency doubling, and self-focusing of light. The electronic origin of the optical susceptibilities is described and the critical power of light self-focusing is estimated for these two crystals.

Ab initio study of ferromagnetic semiconductor Ge1−xMnxTe

First-principles calculations are made on the Ge1−xMnxTe diluted magnetic semiconductors with different compositions. The origin of their ferromagnetism is investigated and the carrier-induced ferromagnetism is developed for these diluted magnetic semiconductors. The Mn 3d states localized with divalent character are deep below the Fermi level, and the carriers introduced by defects are supported in our calculation. The p states of Ge also play an important role in the occurrence of ferromagnetism especially at high temperature. It is thought that Ge1−xMnxTe with a moderate composition (x = 0.51) of Mn atoms is a good candidate for DMS materials.

Ab initio characterization of the electronic and optical properties of a new IR nonlinear optical crystal: K3V5O14

We present detailed investigations of the electronic and optical properties of K3V5O14, including the band structure, density of states (DOS), population analysis, dielectric function, refractive index and second-order nonlinear susceptibilities. The calculations are performed using the ab initio pseudopotential density functional method combined with an anharmonic oscillator model, in which we employ the Perdew–Burke–Eruzerhof form of the generalized gradient approximation together with plane-wave basis sets for expanding the periodic electron density. From the band calculation, K3V5O14 is predicted to be an indirect band gap semiconductor. From the DOS and population analysis, we find that the bonding between K+ and V5O14 layers is mainly ionic while that between V and O is covalent. It is indicated that the hybridization of V-3d with the O-2p states is very important for the optical properties of K3V5O14. The calculated birefringence is large enough to achieve phase-matchable conditions, and our calculated second-harmonic-generation (SHG) coefficients agree with experimental results.

Modeling of configurations and third-order nonlinear optical properties of methyl silsesquioxanes

Configuration optimizations, excited state properties, and the frequency-dependent third-order nonlinear optical polarizabilities have been investigated on a series of methyl-silsesquioxane (MeT) cages [CH(3)SiO(1.5)](n) (n=4, 6, 8, and 10) using ab initio quantum mechanical methods coupled with the sum-over-states methods. The obtained electronic absorption spectra show a redshift as the cage size increases, and the absorption spectra are assigned as charge transfers from oxygen p type to silicon s type atomic orbitals. The calculated average third-order polarizabilities of in the three optical physical processes (third-harmonic generation, the electric-field-induced second-harmonic generation, and degenerate four-wave mixing) have wide nonresonance regions. For all the considered species, the values of gamma decrease in the order of [MeT](4)>[MeT](8)(C(2v))=[MeT](10)>[MeT](6)>[MeT](8)(O(h)).

Enhancements of third-order nonlinear optical response in the triplet excited state of finite open single-walled carbon nanotubes

Spin multiplicity enhancements of third-order nonlinear polarizabilities have been investigated at the excited state for finite single-walled carbon nanotubes (5,0) and (6,0) in terms of the time-dependent density functional theory combined with the sum-over-states method. The time-dependent density functional theory at the B3LYP/3-21G level is employed to calculate the transition moments and the excited state energies of optimized tubes. The obtained results show that the third-order polarizabilities of γ at the excited triplet state are enhanced about from 2 to 3 orders of magnitude and the estimated third-order optical susceptibility of χ(3) is as large as 10−8 esu magnitude order. The electron transitions among the three triplet states make significant contributions to third-order polarizabilities of the (5,0) nanotube, and the electron transition between the two triplet states makes main the contribution to those of the (6,0) nanotube.

Modeling of configurations and third-order nonlinear optical properties of C36 and C34X2 (X=B, N)

Using the ab initio method, the geometrical structures of C(36) and the X (B,N)-doped isomers C(34)X(2) have been optimized. On the basis of the optimized structures, then, the third-order nonlinear optical polarizabilities gamma in the different optical processes of the third-harmonic generation, electric-field induced second-harmonic generation and degenerate four-wave mixing, and two-photon absorption (TPA) cross sections delta are calculated by using TDB3LYP method coupled with the sum-over-states method. The calculated results show that the one-photon allowed excitation process dominate the two-photon excitation process for C(36)-D(6h), whereas the two-photon allowed excitation process dominate the one-photon excitation process for C(36)-D(2d) and C(34)X(2) (B,N). It is found that the largest resonant TPA peaks of dopant fullerenes have a blueshift and the TPA cross sections have an enhancement compared with those of the parent fullerenes of isomers C(36)-D(6h) and C(36)-D(2d).

Band-gap control optical Kerr effect and light self-focusing of semiconducting materials CdxHg1−xGa2S4

We report the dispersion of the optical Kerr effect and the wavelength-dependent critical power of light self-focusing for semiconductors CdxHg1−xGa2S4 in view of the calculated results from the density functional theory combined with an anharmonic oscillator model. It is shown that the third-order optical properties are controlled by the band gaps or cation contents of CdxHg1−xGa2S4, and it is indicated that the optical Kerr effect decreases and the critical power of light self-focusing increases as the x contents and band gaps increase for CdxHg1−xGa2S4.