L-cysteine-assisted synthesis of PbS nanocube-based pagoda-like hierarchical architectures

Nanocube-based pagoda-like PbS hierarchical architectures have been fabricated by hydrothermal treatment of Pb(Ac)(2) and L-cysteine solution. It was suggested that a biomimetic mineralization process happened during the growth of the hierarchical architectures. The biomolecule, L-cysteine, exerts coordination, oriented nucleation of crystals, and the morphology modulating effect. By studying the intermediates of the reaction, we observed that 4-fold symmetric star-shaped microcrystals were formed at first, and a second nucleation process resulted in the generation of nanocube-based pagoda-like hierarchical architectures. By varying the concentration of the reaction system, we got PbS nanocubes and octahedron microcystals. The morphology evolutions of PbS materials are explained by the growth rule of fee nanocrystals. This facile L-cysteine-assisted technique is expected to be employed for the shape-controlled synthesis of other fee structural nanomaterials

受体分子侧基对非富勒烯受体和聚合物给体界面处激子解离速率的影响

最近兴起的以非富勒烯为受体的有机太阳能电池中,给体和受体分子可同时吸收可见太阳光而在各自分子上产生光诱导的激子,这些激子的解离是决定太阳能电池效率的关键因素之一。因此,选取了HXSC12分子为电子给体,6种具有不同侧基的1,8-萘酰亚胺小分子作为电子受体,利用Marcus电子转移速率理论和电子结构计算研究了给体和受体分子上激子在其构成界面上的解离过程,着重分析了受体分子侧基对两种激子解离速率的影响。结果发现给体和受体分子吸收光频率互补,且两种分子上激子解离速率具有相同量级,表明在收集太阳能方面给体和受体具有同等重要的作用。在受体中引入吸电子侧基后,可使得受体吸光强度增加,同时增加了给体-受体界面上激子解离的耦合强度和驱动力从而明显提高激子解离速率。而引入给电子侧基后,吸光强度明显降低,也降低了激子解离的耦合强度,导致激子解离速率降低。本文计算结果与实验观测一致,可为制备高效的有机太阳能电池提供一种思路。国家自然科学基金(21573175,21773191

理论计算研究半导体晶体表面能与能带各向异性对光生电荷分离的影响

利用半导体晶面工程促进电荷分离是提高光催化反应效率的重要措施之一,但如何理解和解释其分离机制还存在诸多争议.针对3个典型的半导体体系TiO2(锐钛矿)、Cu2WS4和SrTiO3,利用密度泛函理论计算,从表面能和体相能带的各向异性这两个角度来探讨它们对光生电子-空穴对分离的影响.结果表明,晶面表面能的差异是发生电荷分离的必要条件,而利用体相能带的各向异性能够解释实验中观测到的电荷分离方向.国家自然科学基金(21573175,21773191

Dissociation rates of H-2 on a Ni(100) surface: the role of the physisorbed state

National Natural Science Foundation of China [21143007, 21203151]; National Basic Research Program of China (973 Program) [2013CB834602]; Foundation of the State Key Laboratory for Physical Chemistry of Solid Surfaces, Xiamen University [201116]The dissociation and recombination rates of physisorbed H-2, and the total dissociation rate of gas phase H-2 on the rigid Ni(100) surface, as well as the corresponding kinetic isotope effects, are calculated by using the quantum instanton method, together with path integral Monte Carlo and adaptive umbrella sampling techniques. Both the dissociation and recombination rates of physisorbed H-2 are dramatically enhanced by the quantum motions of H-2 at low temperatures, for instance, the quantum rates are 43 and 7.5 times larger than the classical ones at 200 K, respectively. For the dissociation of gas phase H-2, at high temperatures, the H-2 can fly over the physisorbed state and dissociate directly, however, at low temperatures, the H-2 is first physisorbed and then dissociates under steady state approximation. The total dissociation rate of gas phase H-2 can be expressed as a combination of the direct and steady state dissociation rates. It has the form of an inverted bell with a minimum value at about 400 K, and detailed analysis shows that the dissociation of gas phase H-2 is dominated by a steady state process below 400 K, however, both the steady state and direct processes are important above 400 K. The calculated kinetic isotope effects reveal that H-2 always has larger rates than D-2 no matter which dissociative process they undergo

Quantum instanton evaluations of surface diffusion, interior migration, and surface-subsurface transport for H/Ni

The quantum instanton approximation is extended to investigate dynamical processes of hydrogen on surface, from surface to subsurface, and between interior sites in nickel lattice. The path integral Monte Carlo and adaptive umbrella sampling techniques are employed to manipulate the quantum instanton formula. The free energy profiles along reaction paths, temperature dependence of free energies, and rates as well as diffusion coefficients are calculated for each process. The results manifest that the motions of nickel atoms beneath the surface have little effect on the hydrogen diffusion on Ni(111), and the hydrogen at the fcc binding site is much easier to get into bulk nickel than the one at the hcp site. The temperature dependence of free energy profiles also reveals that the hydrogen in the subsurface octahedral vacancy and interior tetrahedral vacancy becomes unstable at low temperatures, which proposes a temperature dependence of reaction mechanism. In addition, the relaxations of the lattices dramatically lower the free energy barriers except for the process of the hydrogen diffusion on Ni(111). The quantum motions of the lattice atoms affect the free energies little at 300 K, but they hinder the rates by 20%-40% compared with the classical motions of lattice atoms.National Science Foundation of China [20773115, 20833004]; National Key Basic Research Foundation Program of China [2007CB815204]; Higher Education of China [200803840009

Theoretical studies on absorption, emission, and resonance Raman spectra of Coumarin 343 isomers

The vibrationally resolved spectral method and quantum chemical calculations are employed to reveal the structural and spectral properties of Coumarin 343 (C343), an ideal candidate for organic dye photosensitizers, in vacuum and solution. The results manifest that the ground-state energies are dominantly determined by different placements of hydrogen atom in carboxylic group of C343 conformations. Compared to those in vacuum, the electronic absorption spectra in methanol solvent show a hyperchromic property together with the redshift and blueshift for the neutral C343 isomers and their deprotonated anions, respectively. From the absorption, emission, and resonance Raman spectra, it is found that the maximal absorption and emission come from low-frequency modes whereas the high-frequency modes have high Raman activities. The detailed spectra are further analyzed for the identification of the conformers and understanding the potential charge transfer mechanism in their photovoltaic applications. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3693264]National Science Foundation of China [20833004, 21073146, 21133007]; Research Fund for the Doctoral Program of Higher Education of China [200803840009

Coherent quantum transport in disordered systems: II Temperature dependence of carrier diffusion coefficients from the time-dependent wavepacket diffusion method

NSFC [91333101, 21073146, 21133007]; 973 Program [2013CB834602]; NSF [CHE-1112825]; DARPA [N99001-10-1-4063]; Center of Excitonics; US Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-SC0001088]The time-dependent wavepacket diffusion method for carrier quantum dynamics (Zhong and Zhao 2013 J. Chem. Phys. 138 014111), a truncated version of the stochastic Schrdinger equation/wavefunction approach that approximately satisfies the detailed balance principle and scales well with the size of the system, is applied to investigate the carrier transport in one- dimensional systems including both the static and dynamic disorders on site energies. The predicted diffusion coefficients with respect to temperature successfully bridge from bandlike to hopping-type transport. As demonstrated in paper I (Moix et al 2013 New J. Phys. 15 085010), the static disorder tends to localize the carrier, whereas the dynamic disorder induces carrier dynamics. For the weak dynamic disorder, the diffusion coefficients are temperature-independent (band-like property) at low temperatures, which is consistent with the prediction from the Redfield equation, and a linear dependence of the coefficient on temperature (hopping- type property) only appears at high temperatures. In the intermediate regime of dynamic disorder, the transition from band- like to hopping-type transport can be easily observed at relatively low temperatures as the static disorder increases. When the dynamic disorder becomes strong, the carrier motion can follow the hoppingtype mechanism even without static disorder. Furthermore, it is found that the memory time of dynamic disorder is an important factor in controlling the transition from the band-like to hopping-type motions

Quantum instanton calculation of rate constants for the C(2)H(6) + H -> C(2)H(5) + H(2) reaction: anharmonicity and kinetic isotope effects

Thermal rate constants and kinetic isotope effects for the title reaction are calculated by using the quantum instanton approximation within the full dimensional Cartesian coordinates. The obtained results are in good agreement with experimental measurements at high temperatures. The detailed investigation reveals that the anharmonicity of the hindered internal rotation motion does not influence the rate too much compared to its harmonic oscillator approximation. However, the motion of the nonreactive methyl group in C(2)H(6) significantly enhances the rates compared to its rigid case, which makes conventional reduced-dimensionality calculations a challenge. In addition, the temperature dependence of kinetic isotope effects is also revealed.Scientific Research Foundation of Northwest AF University[Z109021103]; National Science Foundation of China[20833004, 21073146]; Northwest AF Universit

Effects of anharmonicity on diffusive-controlled symmetric electron transfer rates: From the weak to the strong electronic coupling regions

The approach for the diffusive-controlled electron transfer rates [W. Zhu and Y. Zhao, J. Chem. Phys. 126, 184105 (2007)], which is modeled after the Sumi-Marcus theory, is applied to symmetric electron-transfer reactions in a solvent environment with anharmonic potential functions. The electron-transfer rates are evaluated using the quantum R-matrix theory for dealing with the intramolecular vibrational motions and imaginary-time split operator technique for solving the diffusive equations, thereby taking explicit account of the weak-to-strong electronic couplings. The effect of anharmonicity for both the solvent and intramolecular vibrational degrees of freedom are investigated. It is found that the anharmonicity of the intramolecular modes always enhances the rate while the solvent anharmonicity decreases the rate, compared with the harmonic modes. The possible mechanisms have been clarified.National Nature Science Foundation of China [20773115, 20833004]; National Key Basic Research Foundation Program of China [2007CB815204

以生物质气化多联产为核心的区域综合能源系统数学优化模型

基于生物质多联产的综合能源系统(biomass polygeneration integrated energy system,BPIES)将生物质气化多联产与区域BPIES相结合,不但可提高物质与能量综合梯级转换利用效率,同时还兼具节约能源、提高供能质量、增加经济效益等综合效益,体现了生物质能源技术与区域能源规划的深度融合,有望成为最有效、最洁净的生物质能综合利用技术.基于通用数学建模(the general algebraic modeling system,GAMS)软件,在构建生物质气化多联产各模块机理模型基础上,建立了耦合多种可再生与不可再生能源系统的多层次、高维度数学优化模型,在满足区域能源需求的前提下,从经济、环境、技术及能耗等多方面对系统进行综合评估,并结合案例分析验证模型的可靠性与有效性.结果表明,耦合了化学合成单元的BPIES在满足区域负荷与生产化学产品上起到良好的互补作用,不仅能够实现能源的高效利用,还能同时提高系统经济效益.BPIES在4个典型区域的适用性为大连>上海≈广州>昆明.福建省科技计划高新技术与工业科技引导性项目（2018H0036