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1.
A series of heteroleptic cyclometalated Ir(III) complexes for organic light‐emitting diodes (OLEDs) application have been investigated theoretically to explore their electronic structures and spectroscopic properties. The geometries, the electronic structures, the lowest‐lying singlet absorptions and triplet emissions of Ir(dfppy)2(tpip), Ir(tfmppy)2(tpip), and theoretically designed models of Ir(ppy)2(tpip) were investigated with the density functional theory (DFT)‐based approaches, where ppy = 2‐phenylpyridine, dfppy = 4,6‐difluorophenylpyridine, tfmppy = 4‐trifluoromethylphenylpyridine, and tpip = tetraphenylimidodiphosphinate. Their structures in the ground and their excited states have been optimized at the DFT/Becke 3‐parameter Lee Yang Parr (B3LYP)/Los Alamos National Laboratory 2‐double‐z (LANL2DZ) and time‐dependent DFT/B3LYP/LANL2DZ levels, and the lowest absorptions and emissions were evaluated at B3LYP and M062X level of theory, respectively. Furthermore, the energy transfer mechanism together with the advantage of low efficiency roll‐off for these complexes also can be analyzed here. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

2.
In the present work we use a series of Ti–Ru alloys, with minor amounts of Ru (0.01, 0.02, 0.05 and 0.2 at%) to grow anodic self‐organized Ru‐doped TiO2 nanotube layers. When used in dye‐sensitized solar cells (DSSCs), the nanotube layers with an optimum amount of Ru (0.02 at% Ru in the alloy) show a considerable increase in solar cell efficiency (η = 5.2%) under AM1.5 (100 mW/cm2) conditions compared with non‐doped TiO2 nanotubes (η = 4.3%).

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3.
The conformational behavior and structural stability of 2‐fluoro‐6‐nitrotoluene (FNT) were investigated by utilizing density functional theory (DFT) with the standard B3LYP/6‐311 + G** method and basis set combinations. The vibrational wavenumbers of FNT were computed at DFT levels and complete vibrational assignments were made on the basis of normal coordinate calculations. Normal coordinate analysis (NCA) has been carried out to support the vibrational analysis. The results were compared with the experimental values. The observed Fourier transform infrared (FTIR) and Fourier transform (FT) Raman vibrational wavenumbers were analyzed and compared with the theoretically predicted vibrational spectra. The results of vibrational spectra of FNT were also compared with the vibrational spectra of some toluene derivatives. The assignments of bands to various normal modes of the molecules were also carried out. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

4.
周康  冯庆  田芸  李科  周清斌 《计算物理》2018,35(6):702-710
采用密度泛函理论(DFT)体系广义梯度近似(GGA)第一性原理平面波超软赝势方法,分析锐钛矿型TiO2(101)表面吸附NO2分子光学气敏传感的微观机理.结果表明:Cu和Cr原子易于掺入TiO2(101)表面,掺杂表面能稳定地吸附NO2分子且吸附后光学性质发生显著变化.表面吸附NO2分子后,Cu掺杂TiO2(101)表面对分子的吸附能最大,吸附后结构更稳定,分子与表面的距离最短.通过分析差分电荷密度和电荷布居数发现,NO2分子与基底表面间发生电荷转移,转移电子数目:Cu掺杂表面 > Cr掺杂表面 > 无掺杂表面.对比吸收光谱和反射光谱发现,在Cu掺杂表面吸附分子后,光学性质变化最明显,说明表面与吸附分子间氧化还原能力是决定光学气敏传感性能的核心因素.在过渡金属中,Cu与Cr都有4s价电子结构,其4s电子降低了材料表面氧空位的氧化性,增加了其还原性.对于氧化性气体,可以提升表面与分子的氧化还原作用,而Cu的4s电子更加活泼,从而光学气敏传感特性更加明显.因此,Cu掺杂的TiO2对氧化性气体是一种较好的光学气敏传感材料.  相似文献   

5.
关梦雪  廉超  孟胜 《物理学报》2018,67(12):120201-120201
实时密度泛函理论是基于含时Kohn-Sham方程,从实空间实时模拟材料激发态性质的第一性原理计算方法.本文介绍如何利用基于数值原子轨道基的含时密度泛函理论和软件TDAP(Time Dependent Ab initio Package),研究凝聚态物质与光场之间的相互作用.通过引入电磁场的长度规范和速度规范,该方法的适用范围从低维结构拓展到固体材料,且不受微扰论的限制,实现了对大规模、真实凝聚态体系的动力学性质的精确模拟.文中以几个有代表性的工作为例,说明该方法对于研究量子系统中新奇的超快量子动力学现象有着广泛的应用前景.  相似文献   

6.
We present a study of MgSiN2 using soft X‐ray absorption and emission spectroscopy which directly probe the partial density of states. MgSiN2 is new as a host lattice for luminescence materials and used in phosphor‐converted light‐emitting diodes. We compare our measurements to our full potential, all electron density funtional theory calculations. We find excellent agreement between experiment and theory and the band gap of MgSiN2 is measured to be 5.6 ± 0.2 eV in agreement with our calculated value of 5.72 eV. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)  相似文献   

7.
利用密度泛函理论研究了0.25单层(ML),0.5ML,0.75ML和1ML吸附率下H2O在SrTiO3-(001)TiO2表面上的吸附行为.比较了不同吸附率下分子吸附和解离吸附的稳定性,利用微动弹性带(nudged elastic band)方法计算了H2O的解离势垒.结果表明:在低吸附率(0.25ML和0.5ML)时,H2O表现为解离吸附;在0.75ML吸附率下,分子吸附和解离吸附同时存在;而在全吸附(吸附率为1ML)时,分子吸附更稳定.基于对H2O分子与表面之间以及H2O分子之间的电荷转移和相互作用的分析,讨论了吸附率对H2O吸附和解离的影响.  相似文献   

8.
Three derivatives of alkyl anthracene covalently bonded to aza‐18‐crown‐6 at the nitrogen position, anthracene(CH2)n, (n = 1–3) which act as an on–off fluorogenic photoswitch have been theoretically studied using a computational strategy based on density functional theory at B3LYP/6‐31 + G(d,p) method. The fully optimized geometries have been performed with real frequencies which indicate the minima states. The binding energies, enthalpies and Gibbs free energies have been calculated for aza‐18‐crown‐6 ( L ) and their metal complexes. The natural bond orbital analysis is used to explore the interaction of host–guest molecules. The absorption spectra differences between L and their metal ligands, the excitation energies and absorption wavelength for their excited states have been studied by time‐dependent density functional theory with the basis set 6‐31 + G(d,p). These fluorescent sensors and switchers based on photoinduced electron transfer mechanism have been investigated. The PET process from aza‐crown ether to fluorophore can be suppressed or completely blocked by the entry of alkali metal cations into the aza‐crown ether‐based receptor. Such a suppression of the PET process means that fluorescence intensity is enhanced. The binding selectivity studies of the aza‐crown ether part of L indicate that the presence of the alkali metal cations Li+, Na+ and K+ play an important role in determining the internal charge transfer and the fluorescence properties of the complexes. In addition, the solvent effect has been investigated. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

9.
Density‐functional theory (DFT) allows for the calculation of many chemical properties with relative ease, thus making it extremely useful for the physical organic chemistry community to understand and focus on various experiments. However, density‐functional techniques have their limitations, including the ability to satisfactorily describe dispersion interactions. Given the ubiquitous nature of dispersion in chemical and biological systems, this is not a trivial matter. Recent advances in the development of DFT methods can treat dispersion. These include dispersion‐corrected DFT (using explicit, attractive dispersion terms), parameterized functionals, and dispersion‐correcting potentials, all of which can dramatically improve performance for dispersion‐bound species. In this perspective, we highlight the achievements made in modeling dispersion using DFT. We hope that this will provide valuable insight to both computational chemists and experimentalists, who aim to study physical processes driven by dispersion interactions. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

10.
11.
The resonance Raman spectroscopy in conjunction with the density functional theory calculations were used to study the excited state structural dynamics of 2‐mercapto‐1‐methylimidazole (MMI). The experimental UV absorption bands were assigned according to the time‐dependent density functional calculations. The vibrational assignments were done for the A‐band resonance Raman spectra of MMI in water and acetonitrile on the basis of the Fourier transform infrared (FT‐IR) and FT‐Raman measurements in solid, in water and in acetonitrile and the corresponding B3LYP/6‐311+G(d, p) computations. The dynamic structures of MMI were obtained by analysis of the resonance Raman intensity pattern and normal mode analysis. The differences in the dynamic structures of MMI and thiourea were revealed and explained. The structural dynamic of MMI was found to be similar to that of 2‐thiopyrimidone in terms of major reaction coordinates and thus favored the intra‐molecular proton transfer reaction. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

12.
The geometric, energetic, electronic structures and optical properties of ZnO nanowires (NWs) with hexagonal cross sections are investigated by using the first-principles calculation of plane wave ultra-soft pseudo-potential technology based on the density functional theory (DFT). The calculated results reveal that the initial Zn-O double layers merge into single layers after structural relaxations, the band gap and binding energies decrease with the increase of the ZnO nanowire size. Those properties show great dimension and size dependence. It is also found that the dielectric functions of ZnO NWs have different peaks with respect to light polarization, and the peaks of ZnO NWs exhibit a significant blueshift in comparison with those of bulk ZnO. Our results gives some reference to the thorough understanding of optical properties of ZnO, and also enables more precise monitoring and controlling during the growth of ZnO materials to be possible.  相似文献   

13.
冯庆  王寅  王渭华  岳远霞 《计算物理》2012,29(4):593-600
采用基于第一性原理的平面波超软赝势方法研究N和S单掺杂以及N和S共掺杂金红石相TiO2的能带结构,态密度和光学性质.结果表明:N掺杂导致禁带宽度减小为1.43 eV,并且在价带上方形成了一条杂质能带;S掺杂导致费米能级上移靠近导带,直接带隙减小为0.32 eV;N和S共掺杂导致能带结构中出现了两条杂质能带,靠近导带的一条杂质能级距离导带底约0.35 eV,靠近价带的一条杂质能级距离价带顶约0.85 eV,杂质能级主要由N原子的2p轨道和S原子的3p轨道组成.N和S掺杂后不但使TiO2的吸收带产生红移,而且在可见光区具有较大的吸收系数,光催化活性增强.  相似文献   

14.
We present GGA+U calculations to investigate the electronic structure and visible‐light absorption of N,B‐codoped anatase TiO2. The NsBi (substitutional N, interstitial B) codoped TiO2 produces significant Ti 3d and N 2p mid‐gap states when the distance of N and B atoms is far, whereas the NiBi (interstitial N and B) and NsBs (substitutional N and B) codoped TiO2 prefer to form localized p states at 0.3–1.2 eV above the valence band maximum. Further, the optical band edges of the three codoped systems shift slightly to the visible region, but only the far‐distance NsBi codoped TiO2 clearly shows an optical transition. These results indicate that NsBi codoped TiO2 has a dominant contribution to the optical absorption of N,B‐codoped TiO2. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

15.
M A Hadi  M S Ali  S H Naqib  A K M A Islam 《中国物理 B》2017,26(3):37103-037103
In this paper, we perform the density functional theory(DFT)-based calculations by the first-principles pseudopotential method to investigate the physical properties of the newly discovered superconductor LaRu_2As_2 for the first time.The optimized structural parameters are in good agreement with the experimental results. The calculated independent elastic constants ensure the mechanical stability of the compound. The calculated Cauchy pressure, Pugh's ratio as well as Poisson's ratio indicate that LaRu_2As_2 should behave as a ductile material. Due to low Debye temperature, LaRu_2As_2 may be used as a thermal barrier coating(TBC) material. The new compound should exhibit metallic nature as its valence bands overlap considerably with the conduction bands. LaRu_2As_2 is expected to be a soft material and easily machinable because of its low hardness value of 6.8 GPa. The multi-band nature is observed in the calculated Fermi surface. A highly anisotropic combination of ionic, covalent and metallic interactions is expected to be in accordance with charge density calculation.  相似文献   

16.
Jun Ren 《Molecular physics》2013,111(14):1829-1844
We present a detailed study of optical absorption spectra of finite-size structures, using a method based on time-dependent density-functional theory (TDDFT), which involves a self-consistent field for the propagation of the Kohn–Sham wavefunctions in real-time. Although our approach does not provide a straightforward assignment of absorption features to corresponding transitions between Kohn–Sham orbitals, as is the case in frequency-domain TDDFT methods, it allows the use of larger timesteps while conserving total energy and maintaining stable dipole moment oscillations. These features enable us to study larger systems more efficiently. We demonstrate the efficiency of our method by applying it to a hydrogen-terminated silicon cluster consisting of 364 atoms, with and without P impurities. For cases where direct comparison to experiment can be made, we reproduce the absorption features of fifteen small molecules [N2, O2, O3, NO2, N2O, NH3, H2O, H2CO, H2CO3, CO2, CH4, C2H2, C2H4, C2H6, C6H6] and find generally good agreement with experimental measurements. Our results are useful for the detection and the determination of orientation of these molecules.  相似文献   

17.
Carbazole derivatives have drawn increasing attention recently in organic electronic device applications because of their particular optoelectronic properties. An in‐depth theoretical investigation was elaborated in this paper to reveal the molecular structures, optoelectronic properties, and the structure‐property relationships of different carbazole‐linked functional groups. The geometric and electronic structures in ground and the mobility for the hole and electron are both calculated by density functional theory method. The excited‐state geometries of these compounds were obtained through Single‐excitation Configuration Interaction method, and time‐dependent density functional theory calculation results described the absorption and emission spectra properties, respectively. Some conclusions are as follows: (1) enlarging the π‐conjugated area, the corresponding spectra red shifted markedly; (2) by introducing the electron‐donor such as carbazole, the spectra blue shifted slightly; (3) compared with compound 1, the spectra for these compounds are hardly influenced by introducing an electron‐acceptor or heterocyclic substitution. On all accounts, these compounds are interesting optoelectronic functional materials. On the basis of their structural modifiability, the arylamine derivatives substituted carbazole compounds have great potential in the applications of organic light‐emitting diodes, organic solar cells, and sensors. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

18.
This study reports a facial regio‐selective synthesis of 2‐alkyl‐N‐ethanoyl indoles from substituted‐N‐ethanoyl anilines employing palladium (II) chloride, which acts as a cyclization catalyst. The mechanistic trait of palladium‐based cyclization is also explored by employing density functional theory. In a two‐step mechanism, the palladium, which attaches to the ethylene carbons, promotes the proton transfer and cyclization. The gas‐phase barrier height of the first transition state is 37 kcal/mol, indicating the rate‐determining step of this reaction. Incorporating acetonitrile through the solvation model on density solvation model reduces the barrier height to 31 kcal/mol. In the presence of solvent, the electron‐releasing (–CH3) group has a greater influence on the reduction of the barrier height compared with the electron‐withdrawing group (–Cl). These results further confirm that solvent plays an important role on palladium‐catalyzed proton transfer and cyclization. For unveiling structural, spectroscopic, and photophysical properties, experimental and computational studies are also performed. Thermodynamic analysis discloses that these reactions are exothermic. The highest occupied molecular orbital?lowest unoccupied molecular orbital gap (4.9–5.0 eV) confirms that these compounds are more chemically reactive than indole. The calculated UV–Vis spectra by time‐dependent density functional theory exhibit strong peaks at 290, 246, and 232 nm, in good agreement with the experimental results. Moreover, experimental and computed 1H and 13C NMR chemical shifts of the indole derivatives are well correlated. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

19.
雷军辉  王秀峰  林建国 《中国物理 B》2017,26(12):127101-127101
Based on the density functional calculations, the structural and electronic properties of the WS_2/graphene heterojunction under different strains are investigated. The calculated results show that unlike the free mono-layer WS_2, the monolayer WS_2 in the equilibrium WS_2/graphene heterojunctionis characterized by indirect band gap due to the weak van der Waals interaction. The height of the schottky barrier for the WS_2/graphene heterojunction is 0.13 eV, which is lower than the conventional metal/MoS_2 contact. Moreover, the band properties and height of schottky barrier for WS_2/graphene heterojunction can be tuned by strain. It is found that the height of the schottky barrier can be tuned to be near zero under an in-plane compressive strain, and the band gap of the WS_2 in the heterojunction is turned into a direct band gap from the indirect band gap with the increasing schottky barrier height under an in-plane tensile strain. Our calculation results may provide a potential guidance for designing and fabricating the WS_(2~-)based field effect transistors.  相似文献   

20.
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