- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Optimizing the conductance switching performance in photoswitchable dimethyldihydropyrene/cyclophanediene single-molecule junctions
摘要： Designing molecular switches with high stability and performance is still a great challenge in the field of molecular electronics. For this aim, key factors influencing the charge transport properties of molecular devices require to be carefully addressed. Here, by using the nonequilibrium Green’s function method in combination with the density functional theory, effect of bridging manner (i.e., linkage sites) for dimethyldihydropyrene (DHP)/cyclophanediene (CPD) photoswitchable molecule sandwiched between two Au(111) electrodes has been theoretically investigated. The computational results show that the fully conjugated DHP is more conductive than the less conjugated CPD, manifesting an evident switching effect. It is also found that the ON/OFF switching performance of DHP/CPD is dramatically modulated by the bridging manner. Further analysis attributes the switching feature to the different alignments of conducting HOMO with the Fermi energy for DHP and CPD. And it also reveals that local bond contributions to the electron transmission pathway are closely related to both the conjugation characteristics and bridging manner of the core molecule. This work suggests that the bridging manner of core molecule in single-molecule junction plays an essential role in determining the switching performance and should be carefully addressed in future design of molecular switches.
关键词： Single-molecule switch,Density functional theory,Nonequilibrium Green’s function method
更新于2025-09-23 15:23:52
-
Theoretical Study on Adsorption Characteristics and Environmental Effects of Dimetridazole on TiO2 Surface
摘要： In this paper, the adsorption characteristics of dimetridazole on anatase TiO2(101) and (001) crystal surfaces has been studied by using density functional theory. Adsorption structures of dimetridazole on anatase TiO2(101) and (001) crystal surfaces have been optimized under vacuum, water, acidic and alkaline conditions, respectively. The optimum adsorption site, adsorption energy and the electronic structure of the stable adsorption model were calculated. By analyzing the optimal adsorption site, we found that the possibility of degradation of dimetridazole on the surface of TiO2 and reaction site of degradation were the opening ring of C-N bond on the imidazole ring. By comparing the adsorption characteristics of dimetridazole on two different crystal planes of TiO2 under acidic and alkaline conditions, we found that the adsorption wavelengths of electron transition between conduction bands and valence bands of dimetridazole on anatase TiO2(101) crystal plane are within the range of visible wavelength. The results show that TiO2(101) can effectively utilize visible light and catalyze the adsorption and degradation reaction of dimetridazole on TiO2(101) surface. Our results show that TiO2(101) crystal surface can effectively use visible light under acidic and alkaline conditions. Our conclusion can explain the experimental result that the use of visible light on TiO2(001) face is greatly affected by the environment.
关键词： Dimetridazole,Density functional theory,TiO2 Photocatalyst,Explanation
更新于2025-09-23 15:23:52
-
Effect of acceptor moieties on static and dynamic first hyperpolarizability of azobenzene chromophores
摘要： The effect of acceptor on static and dynamic first hyperpolarizability, β, of trans- and cis-isomers of azochromophores AAB-DCV and AAB-TCV is studied. Calculations were performed by MP2 and DFT with three density functionals: M06-2X, CAM-B3LYP and ωB97X-D in gas phase and chloroform. Dynamic first hyperpolarizabilities were calculated by TD-DFT at 1.165 and 0.65 eV. The first hyperpolarizability values for trans-isomers are approximately three times greater than those for cis-isomer; solvent effect is essential comprising 2.7 and 3.2 times growth for static values for AAB-DCV and AAB-TCV, respectively, the corresponding dynamic estimations for βtot(2ω) being slightly smaller (2.2 and 2.6 times).
关键词： Dynamic characteristics,MP2,Azochromophore,Solvent effect,Acceptor effect,First hyperpolarizability,Density functional theory,TD-DFT
更新于2025-09-23 15:23:52
-
Exploring approximate geometries of minimum energy conical intersections by TDDFT calculations
摘要： An approach is proposed to obtain approximate geometries for minimum energy conical intersections between the ground and first excited singlet electronic states (S0/S1-MECIs) using the time-dependent density functional theory (TDDFT). This approach uses the energy shift method to avoid discontinuities on TDDFT potential energy surfaces around conical intersections. It is shown numerically that the approximate S0/S1-MECIs of benzene and naphthalene obtained by this approach qualitatively reproduce the geometries and energies of the S0/S1-MECIs obtained by multireference theories. Moreover, the performance of the present approach when combined with an automated MECI searching method is examined through applications to benzene and naphthalene.
关键词： energy shift method,time dependent density functional theory,gradient projection,single component artificial force induced reaction,conical intersection,global reaction route mapping
更新于2025-09-23 15:23:52
-
Acceptor levels of the carbon vacancy in 4 <i>H</i> -SiC: Combining Laplace deep level transient spectroscopy with density functional modeling
摘要： We provide direct evidence that the broad Z1/2 peak, commonly observed by conventional deep level transient spectroscopy in as-grown and at high concentrations in radiation damaged 4H-SiC, has two components, namely, Z1 and Z2, with activation energies for electron emissions of 0.59 and 0.67 eV, respectively. We assign these components to Z?1/2 + e? → Z?1/2 → Z?1/2 + 2e? transition sequences from negative-U ordered acceptor levels of carbon vacancy (V_C) defects at hexagonal/pseudo-cubic sites, respectively. By employing short filling pulses at lower temperatures, we were able to characterize the first acceptor level of V_C on both sub-lattice sites. Activation energies for electron emission of 0.48 and 0.41 eV were determined for Z1(?/0) and Z2(?/0) transitions, respectively. Based on trap filling kinetics and capture barrier calculations, we investigated the two-step transitions from neutral to doubly negatively charged Z1 and Z2. Positions of the first and second acceptor levels of V_C at both lattice sites, as well as (?/0) occupancy levels, were derived from the analysis of the emission and capture data.
关键词： density functional theory,acceptor levels,deep level transient spectroscopy,negative-U ordering,carbon vacancy,4H-SiC
更新于2025-09-23 15:23:52
-
Cobalt doping-induced strong electromagnetic wave absorption in SiC nanowires
摘要： Understanding the electronic structure-property relationship in doped systems is a prerequisite to designing functional materials. We fabricated Co-doped SiC nanowires with different Co contents by a facile carbothermal reduction approach. The nanowires were characterized in terms of microstructure, electronic structure, and electromagnetic (EM) parameters to uncover the effect of Co dopants on enhancing the EM wave absorption ability. Microstructure analysis and density functional theory calculations verified that the doped Co species inhibited the formation of stacking faults and point defects and increased the conductivity of Co-doped SiC nanowires, which indicated the dominant role of conductivity in enhancing dielectric loss. The Co dopants also imparted the Co-doped SiC nanowires with distinct room-temperature ferromagnetic property, which led to enhanced magnetic loss and impedance matching. The induced synergism among SiC nanowires and Co dopants endowed Co-doped SiC nanowires with strong EM wave absorption ability. The minimum reflection loss of Co-doped SiC nanowires reaches (cid:1)50 dB, and the effective absorption bandwidth is 4.0 GHz with only 1.5 mm sample thickness. Thus, Co-doped SiC nanowires can be used as effective EM wave absorption materials. This study also provided a guideline for designing high-performance EM wave absorbers.
关键词： Dielectric loss,Doping,Density functional theory calculations,Electromagnetic wave absorption,Magnetic property
更新于2025-09-23 15:23:52
-
Effect of external stresses on the optical and electronic properties of potassium dihydrogen phosphate crystals
摘要： Potassium dihydrogen phosphate (KDP) has been extensively used in electro-optic switches and laser spectroscopy in modulating the frequency of laser radiation. When making refined optical KDP components for such applications, the external stresses in the manufacturing process can introduce changes in their optical and electronic properties. With the aid of the ab initio density functional theory analysis, this paper investigates the effect of stresses on the absorption coefficient, band gap, refractive index, dielectric function and Plasmon energy. It was found that the stress-induced variations in these properties are due to a change of KDP molecular structures. The microstructural changes induced by the uniaxial (along the <110> direction) or by the biaxial (<100> and <010> directions) or by the triaxial (<100>, <010> and <001> directions) tensile stresses bring about significant changes in the optical and electronic properties of KDP.
关键词： Density functional theory,Potassium dihydrogen phosphate,optical properties,stress
更新于2025-09-23 15:23:52
-
Synthesis, characterization and photophysical properties of a new class of pyrene substituted 1,3,4-oxadiazole derivatives
摘要： We have designed and synthesized a series of a new class of pyrene substituted 1,3,4- oxadiazole derivatives (abbreviated as 3(a-e)) through palladium catalyzed Suzuki-Miyaura cross coupling reaction. The chemical structures of the probes were characterized by using analytical techniques namely 1H NMR, 13C NMR, FT-IR and GC-MS. The novel bipolar molecules consist of pyrene as an electron donor unit (D) and electron-deficient 1,3,4-oxadiazole as an acceptor unit (A) linked via extending π conjugation through a phenyl spacer with para linkages (D-π-A). Intramolecular charge transfer is improved by structure-property relationship. The detailed photophysical/solvatochromic properties of newly synthesized derivatives have been studied employing steady state spectroscopic techniques. The photophysical studies revealed that compounds emit strong indigo-blue fluorescence and efficient blue emission extending into blue-green in solid phase with high quantum yields. Thermal and morphological stabilities of the derivatives were studied employing DSC and TGA measurements. In addition, density functional theory (DFT) computations have been carried out to demonstrate various intramolecular interactions that cause the stabilization of the compound leading to its optoelectronic applications. The highest occupied molecular orbital energy (HOMOs), lowest unoccupied molecular orbital energy (LUMOs), the energy bandgap, chemical hardness (η), softness (δ), electronegativity (χ) and chemical potential (μ) were computed with the help of frontier molecular orbitals. The results were compared and discussed with the experimental results. The results demonstrate that the novel pyrene containing oxadiazole derivatives could be used as small organic molecules for multifunctional organic light-emitting devices (OLED)/optoelectronic devices.
关键词： Intramolecular charge transfer (ICT),1,3,4-Oxadiazole,Quantum yield,Pyrene,Density functional theory
更新于2025-09-23 15:23:52
-
Unusual pressure-induced electronic structure evolution in organometal halide perovskite predicted from first-principles
摘要： Pressure has been demonstrated to be an effective parameter to alter the atomic and electronic structures of materials. By using the first-principles calculations based on density functional theory (DFT), we systematically investigated the changes in the atomic and electronic structures of the cubic MAPbI3 phase under pressures. It is found that the band gap of the compressed cubic MAPbI3 structure exhibits a remarkable redshift to 1.114/1.380 eV in DFT/HSE-SOC calculation under a mild pressure of 2.772 GPa, and subsequently shows a widening at higher pressures until ~20 GPa. As the pressure further increases, the band gap closes at ~80 GPa. Detailed structural and electronic characteristic analyses indicate that the band gap of the cubic MAPbI3 structure is determined by two competing effects: the lattice contraction decreases its band gap while the PbI6 octahedral tilting increases it. Given that, pressure can be a powerful tool to help understanding the optoelectronic properties of perovskite materials.
关键词： Density functional theory,Pressure,Organometal halide perovskite,Electronic structure
更新于2025-09-23 15:23:52
-
Ab initio calculation of antimony sulphide nanowire
摘要： We have performed first-principles calculations on orthorhombic antimony sulphide (Sb2S3) nanowire using full-potential linearized augmented plane wave (FP-LAPW) method based on the density-functional theory (DFT) as implemented in WIEN2k package to investigate the electronic and optical properties. Engel–Vosko generalized gradient approximation (EV-GGA) is used as exchange-correlation functional. The nanowire is simulated in the [001] direction with vacuum in two directions using supercell method. The results are compared with Sb2S3 bulk in our pervious calculation. We have found that the electronic and optical properties significantly change in Sb2S3 nanowire. The density of state (DOS) for Sb2S3 nanowire calculated is higher than bulk Sb2S3 and from the electronic band structure, the indirect band gap is about 0.12 eV where this value is much lower than Sb2S3 bulk. However, this value is much lower than experimental value. The optical properties including absorption coefficient, reflectivity, refractive index and energy loss function are derived from the calculated complex dielectric for photon energy up to 20 eV to understand the optical behavior of Sb2S3 in one-dimensional (1-D) nanostructure. From analysis, the optical response of Sb2S3 nanowire demonstrate quite interesting optical behavior for one-dimension (1-D) nanostructure. The absorption coefficient for Sb2S3 nanowire is considerably higher in visible light range than Sb2S3 bulk.
关键词： optical properties,Antimony Sulphide,Density Functional Theory,LAPW,nanowire,electronic structure
更新于2025-09-23 15:23:52