林区灯下蛾类多样性研究

鳞翅目昆虫(包括蝶类和蛾类)是生态系统中种类丰富的一类昆虫,是食物链(网)中的重要环节,与生境内植物群落有很密切的功能联系,在生态系统的结构和功能中具有重要作用。本文通过2011年6月～9月,对湖南省八大公山国家级自然保护区蛾类昆虫进行了系统的调查研究,意在分析该地区蛾类现状以及多样性分布情况。

Electronic and Optical Properties of O-Terminated Armchair Graphene Nanoribbons

The structure, electromagnetic and optical properties of the O-terminated graphene nanorib- bons with armchair edge are studied using first-principles theory. The results show that the O-terminated armchair edge are more stable than the H-terminated ribbons and show metal- lic character. Spin-polarized calculations reveal that the antiferromagnetic state are more stable than the ferromagnetic state. The energy band and density of states analyses show that the O-terminated armchair edge are antiferromagnetic semiconductors. Because of the terminated 0 atoms, the dielectric function has an evident red shift and the first peak is the strongest with its main contribution derived from the highest valence band. The peaks of the dielectric function, reflection, absorption, energy loss are related to the transition of electrons. Our results suggest that the O-terminated graphene nanoribbons have potential applications in nanoelectronics, opto-electric devices.

First-principles investigations of structural, mechanical, electronic and optical properties of U_3Si_2-type AlSc_2Si_2 under high pressure

The structural, elastic, electronic and optical properties for U3Si2-type AlSc2Si2 compound under pressure were systematically investigated by using the first-principles calculations. The values of elastic constants and elastic moduli indicate that AlSc2Si2 keeps mechanical stability under high pressure. The mechanical properties of AISc2Si2 are compared with those of Al3Sc. The results indicate that AlSc2Si2 is harder than AI3Sc. Anisotropic constant AU and 3D curved surface of elastic moduli predict that AISc2Si2 is obviously anisotropic under pressure. The electronic structure of AlSc2Si2 exhibits metallic character and the metallicity decreases with the elevated pressure. In addition, optical properties as a function of pressure were calculated and analyzed. The present work provides theoretical support for further experimental work and industrial applications.

First-principles Study on Enhanced Optical Stability of BaMgAl10O17：Eu^2＋ Phosphor by SiN Doping

Using density functional theory, we studied band structure, density of states, optical proper- ties and Mulliken population of the pure and SiN doped BaMgAl10017：Eu^2＋ （BAM：Eu^2＋） phosphors. Calculation results showed that the bands of BAM：Eu2＋ were of low band energy dispersion, indicating large joint density of states, hence high performance of optical absorption and luminescence. BAM：Eu^2＋ showed stronger absorption intensity while Eu^2＋ occupied the BR sites instead of the mO sites. The concentration of Eu^2＋ at BR sites increased while that at mO sites decreased after Si-N doping. The influence of the variation of Eu^2＋ distribution on the spectra was stronger than the influence of the decrease of Eu^2＋ PDOS when SiN concentration was lower than 0.25, therefore the absorption and luminescence intensity of BAM：Eu^2＋ were enhanced. Mulliken population of Si-N bond was higher than A1-O bond, while that of Eu-N bond was higher than Eu-O bond as well, indicating that Si-N bonds and Eu-N bonds possessed higher covalence than Al-O bonds and Eu-N bonds respectively. The existence of Si-N bonds and Eu-N bonds enhanced the local covalence of Eu^2＋, hence the optical stability of BAM：Eu^2＋.

Field controllable electronic properties of MnPSe_(3)/WS_(2) heterojunction for photocatalysis

Transition metal dichalcogenides are interesting candidates as photocatalysts for hydrogen evolution reaction.The MnPSe_(3)/WS_(2) heterostructure is hence studied here with first principles calculations by exploring its electronic properties under the application of an electric field.It is discovered that the band gap will decrease from the WS_(2) monolayer to the MnPSe_(3)/WS_(2) heterostructure with Perdew-Burke-Ernzerhof functional,while increase slightly when electron correlation is involved.The conduction band minimum of the heterostructure is determined by the MnPSe3 layer,while the valence band maximum is contributed by the WS_(2)layer.The band edges and band gap suggest that the heterostructure will have good photocatalytic properties for water splitting.Moreover,comparing to monolayer WS_(2),the light absorption in both the ultraviolet and visible regions will be enhanced.When an electric field is present,a linear relation is observed between the electric field and the band gap within specific range,which can thus modulate the photocatalytic performance of this heterostructure.

First-Principles Investigation on Triazine Based Thermally Activated Delayed Fluorescence Emitters

Three kinds of triazine based organic molecules designed for thermally activated delayed fluorescence （TADF） emitters are investigated by first-principles calculations. An optimal Hartree-Fork （HF） method is adopted for the calculation of energy gap between the first singlet state （S1） and the first triplet state （T1）. The natural transition orbital, the electron- hole （e-h） distribution and the e-h overlap diagram indicate that the S1 states for the three systems include both charge-transfer and some localized excitation component. Further quantitative analysis of the excitation property is performed by introducing the index Ar and the integral of e-h overlap S. It is found that symmetric geometry is a necessary condition for TADF emitters, which can provide more delocalized transition orbitals and consequently a small S1-T1 energy gap. Artful inserting aromatic groups between donors and acceptors can significantly enhance the oscillator strength. Finally, the energy state structures calculated with the optimal HF method is presented, which can provide basis for the study of the dynamics of excited states.

Electron-Helium Atom Collisions in the Presence of a Bichromatic Laser Field

The differential cross section （DCS） for electron-helium atom collisions in the presence of a bichromatic CO2 laser field is investigated as a function of the scattering angle θ by employing first-Born approximation （FBA） with a simple screening electric potential. We discuss in detail the influence of the scattering geometry, the photon energy and the number of photons exchanged on the DCSs. These illustrate that the three factors have important effects on the elastic scattering and the screening electric potential is effective.

Detection of Electronic Coherence via Two-Dimensional Electronic Spectroscopy in Condensed Phase

Two dimensional Fourier transforrn electronic spectroscopy （2DES） in the visible region enables direct observation of complex dynamics of molecules including quantum coherence in the condensed phase. This review aims to provide a bridge between the principles and intuitive physical description of 2DES for tutorial purpose. Special emphasis is laid upon how 2DES circumvents the restrictions from both uncertainty principle and the wave-packet collapse during the coherent detection, leading to the successful detection of the coherence in terms of energy difference between the eigenstates showing as the quantum beats; then upon the possible mixing among the pure electronic transition, single-rnode and multi-mode coupled vibronic transition leading to the observed beating phenomena. Finally, recent ad- vances in experimentally distinguishing between the electronic coherence and the vibrational coherence are briefly discussed.

The Effect of Oxidation/Reduction Disposing on Optical Properties of Mg:Fe:Mn:LiNbO_3 Crystals

The congruent tri-doped Mg:Mn:Fe:LiNbO 3 crystal has been grown by Czochralski method. Some crystal samples are reduced in Li 2CO 3 powder at 500 ℃ for 24 hours or oxidized for 10 hours at 1100 ℃ in Nb 2O 5 powder. Compared with As-grown Mg:Mn:Fe:LiNbO 3, the absorption edge in UV-Vis. absorption spectrum of the oxidized sample and the reduced shifts to the violet and the red, respectively. Reduction increases the absorption of crystals in visible light region. In two-wave coupling experiments, the writing time, maximum diffraction efficiency and the erasure time of crystal samples in the same conditions are determined. The results indicate that oxidation and reduction disposing has great effect on the holographic recording properties of these crystals. The reduced crystal exhibits the fastest response time of 160 s among the crystal series. The mechanism of post-disposing effect on the holographic recording properties of Mg:Mn:Fe:LiNbO 3 crystals are investigated.

SGC Switching Between Subluminal to Superluminal Propagation in V-Type Atom

For a V-type three-level atomic system with two closely spaced upper levels, we investigate the light pulse propagation properties with only one laser field. Due to spontaneously generated coherence, the group velocity of the light pulse can be changed from subluminal to superluminal. The effects of the field intensity and the two-upper level splitting on the group velocity are also shown. At last, an analytical expression for the group velocity is given in the case of a weak field.

g-C3N4/SnS2 Heterostructure： a Promising Water Splitting Photocatalyst

Graphite-like carbon nitride （g-C3N4） based heterostrutures has attracted intensive attention due to their prominent photocatalytic performance. Here, we explore the g-CaN4/SnS2 coupling effect on the electronic structures and optical absorption of the proposed g-CaN4/SnS2 heterostructure through performing extensive hybrid functional calculations. The obtained geometric structure, band structures, band edge positions and optical absorptions clearly reveal that the g-C3N4 monolayer weakly couples to SnS2 sheet, and forms a typical van der Waals heterojunction. The g-C3N4/SnS2 heterostructure can effectively harvest visible light, and its valence band maximum and conduction band minimum locate in energetically favorable positions for both water oxidation and reduction reactions. Remarkably, the charge transfer from the g-C3N4 monolayer to SnS2 sheet leads to the built-in interface polarized electric field, which is desirable for the photogenerated carrier separation. The built-in interface polarized electric field as well as the nice band edge alignment implys that the g-CaN4/SnS2 heterostructure is a promising g-CaN4 based water splitting photocatalyst with good performance.

Electronic Structure and Optical Properties of Zinc-Blende In_xGa_(1-x)N_yAs_(1-y) by a First-Principles Study

Electronic structure and optical properties of the zinc-blende InxGa1-xNyAs1-y system are calculated from the first-principles. Some relative simulations are performed using CA-PZ form of local density approximation in the framework of density functional theory. The supercell of intrinsic GaAs is calculated and optimized by using different methods, and the LDA-CA-PZ gives the most stable structure. The band gap of InzGa1-x As tends to decrease with the increasing In concentration. For the case of In0.0625Ga0.9375NyAs1-y, the band gap will show slight difference when N concentration is larger than 18. 75~. The optical transition of In dopant in GaAs exhibits a red shift, while it is a blue shift for the N dopant in InGaAs. Besides, dielectric function, reflectivity, refractive index and loss function in different doping model of InxGa1-xNyAs1-y are also discussed.

First-principle study of electronic structure and optical properties of Au-doped VO2

The electronic structure and optical properties of VO2 and Au-VO2 were studied using density functional theory. The calculation results show that the interaction between Au and O is stronger than that between V and O. There exists not only the covalent bonding but also ionic bonding in Au--O bond. The band gap of Au-VO2 is smaller than that of VO〉 while the dielectric constant, conductivity, and intensity of optical absorption of Au-VO2 are larger than those of VO2.

Local Structures and Chemical Properties of Deprotonated Arginine

The potential energy surface of gaseous deprotonated arginine has been systematically in- vestigated by first principles calculations. At the B3LYP/6-31G（d） level, apart from the identification of several stable local structures, a new global minimum is located which is about 6.56 k J/tool more stable than what has been reported. The deprotonated arginine molecule has two distinct forms with the deprotonation at the carboxylate group （COO-）. These two forms are bridged by a very high energy barrier and possess very different IR spectral profiles. Our calculated proton dissociation energy and gas-phase acidity of argi- nine molecule are found to be in good agreement with the corresponding experimental results. The predicted geometries, dipole moments, rotational constants, vertical ionization energies and IR spectra of low energy conformers will be useful for future experimental measurements.

Influence of Be-Doping on Electronic Structure and Optical Properties of ZnO

The electronic structure and optical properties of Zn1-x BexO alloys were studied using first principle calculation based on density functional theory （DTF）. The results indicate that the band gap of Zn1-x BexO alloys increases as Be composition increases. The major reason is that the valence band maximum （VBM） of O2p has no obvious shift while the conduction band minimum （CBM） of Zn4s shifts to higher energy as x composition increases. Calculated results of the imaginary part of the dielectric function reveal that the peak heights at 2.0 and 6.76eV decrease as x composition increases, which is attributed to the decrease of the Zn3d states after Be substitutes for Zn. Due to the increasing transition probability from VBM of O2p to CBM of Be2s in wurtzite structure BeO,the peak height at 9.9eV is enhanced and its position shifts toward higher energy.

[C(NH)]PO·2HO: A new metal-free ultraviolet nonlinear optical phosphate with large birefringence and second-harmonic generation response

[PO_(4)]3-possesses small microscopic secondorder susceptibility and polarizability anisotropy,which inherently result in weak second-harmonic generation (SHG)and small birefringence.Herein,a new noncentrosymmetric phosphate,[C(NH_(2))3]3PO_(4)·2H_(2)O,was successfully designed and synthesized by a solution evaporation method.[C(NH_(2))3]3PO_(4)·2H_(2)O without metal ions is composed of planar conjugated guanidine cations and PO_(4)tetrahedrons,which are connected by hydrogen bonds,forming a three-dimensional network.Physical property measurements indicate that the title compound displays an SHG response of 1.5×KH_(2)PO_(4)(KDP) and a larger birefringence (0.055@546.1 nm)compared with most reported ultraviolet nonlinear optical phosphates.Furthermore,first-principles calculations reveal that theπ-conjugated planar[C(NH_(2))3]+cations and[PO_(4)]3-groups are responsible for its excellent linear and NLOproperties.

Synthesis, characterization, and theoretical analysis of three new nonlinear optical materials K7MRE2B15O30（M= Ca and Ba, RE= La and Bi）

Three new complex borate compounds K7CaBi2B15O30, K7CaLa2B15 O30 and K7BaBi2B15O30 have been synthesized by the high-temperature solution method.K7CaLa2B15O30and K7CaBi2B15O30crystallize in the chiral trigonal space group R32, while K7BaBi2B15O30 crystallizes in the noncentrosymmetric orthorhombic polar space group Pca21. All of the title compounds have similar three-dimensional crystal structures, which are composed of isolated B5 O10 groups and LaO6 or BiO6 octahedra, and K^+, Ca^2+, and Ba^2+ cations fill into the cavities to keep charge balance. Based on our research, in the system of K7 MIIRE2 B15O30(MII= Ca, Sr,Ba, Zn, Cd, Pb, K/RE0.5;RE = Sc, Y, La, Gd, Lu, Bi),K7BaBi2B15O30 is unique and crystallizes in a different space group, which enriches the structural chemistry of borate.Detailed structural analyses indicate that the structural variation is due to the difference in size and coordination number of the alkaline-earth metal cations. Besides, UV-Vis-NIR spectroscopy analysis and the second-harmonic generation(SHG) measurement on the powder samples show that K7CaBi2B15O30 exhibits a UV cutoff edge(about 282 nm) and a moderate SHG response(about 0.6 × KDP). In addition,thermal analysis and infrared spectroscopy were also presented. To better understand the structure-property relationships of the title compounds, the first-principles calculations have been performed.

First-principles calculations of optical properties of Mg_2Pb

Based on the density functional theory （DFT）, the electronic structures and optical properties of Mg2Pb are calculated by using the local density approximation （LDA） and plane wave pseudo-potential method. The calculation results show that the indirect band gap width of Mg2Pb is 0.02796 eV. The optical properties of MgzPb have isotropic characteristics, the static dielectric function of Mg2Pb is ε1（0） = 10.33 and the refractive index is n0 = 3.5075. The maximum absorption coefficient is 4.8060×10^5 cm-1. The absorption in the photon energy range of 25-40 eV approaches to zero, shows the optical colorless and transparent behaviors.

First-principles study on electronic structures and optical properties of the single-walled (n, 0) ZnO nanotubes

Using the first-principles calculations, we studied the geometric structures, electronic structures and optical properties of the single-walled (n, 0) ZnO nanotubes (NTs). The calculated results show that all the bind energies of the single-walled (n,0) ZnO NTs are of negative values, which indicate that the ZnO NTs can exist stably as single-walled NTs. While the calculated results of electronic structure indicate that the single-walled (n,0) ZnO NTs are a type of direct wide band-gap semiconductor materials, the whole valence bands are spread and drift to low-energy direction with the increase of the NT diameter. The defect energy levels caused by quantum size and surface effects emerge on the top of the valence bands. Furthermore, the calculated results of optical properties reveal that the dielectric peaks have a blue shift and the edge of absorption band corresponds to ultraviolet band with the decrease of the NT diameter. The single-walled (n, 0) ZnO NTs can be applied to ultraviolet semiconductor systems.

Piezoelectricity in two-dimensional group-Ill monochalcogenides

It is found that several layer-phase group-III monochalcogenides, including GaS, GaSe, and InSe, are piezoelectric in their monolayer form. First-principles calculations reveal that the piezoelectric coefficients of monolayer GaS, GaSe, and InSe （2.06, 2.30, and 1.46 pm-V-1） are of the same order of magnitude as previously discovered two-dimensional （2D） piezoelectric materials such as boron nitride （BN） and MoS2 monolayers. This study therefore indicates that a strong piezoelectric response can be obtained in a wide range of two-dimensional materials with broken inversion symmetry. The co-existence of piezoelectricity and superior photo-sensitivity in these monochalcogenide monolayer semiconductors means they have the potential to allow for the integration of electromechanical and optical sensors on the same material platform.