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Growth-Rule-Guided Structural Exploration of Thiolate-Protected Gold Nanoclusters
摘要： Understanding the structure and structure?property relationship of atomic and ligated clusters is one of the central research tasks in the field of cluster research. In chemistry, empirical rules such as the polyhedral skeleton electron pair theory (PSEPT) approach had been outlined to account for skeleton structures of many main-group atomic and ligand-protected transition metal clusters. Nonetheless, because of the diversity of cluster structures and compositions, no uniform structural and electronic rule is available for various cluster compounds. Exploring new cluster structures and their evolution is a hot topic in the field of cluster research for both experiment and theory. In this Account, we introduce our recent progress in the theoretical exploration of structures and evolution patterns of a class of atomically precise thiolate-protected gold nanoclusters using density functional theory computations. Unlike the conventional ligand-protected transition metal compounds, the thiolate-protected gold clusters demonstrate novel metal core/ligand shell interfacial structures in which the Aum(SR)n clusters can be divided into an ordered Au(0) core and a group of oligomeric SR[Au(SR)]x (x = 0, 1, 2, 3, ...) protection motifs. Guided by this “inherent structure rule”, we have devised theoretical methods to rapidly explore cluster structures that do not necessarily require laborious global potential energy surface searches. The structural predictions of Au38(SR)24, Au24(SR)20, and Au44(SR)28 nanoclusters were completely or partially verified by the later X-ray crystallography studies. On the basis of the analysis of cluster structures determined by X-ray crystallography and theoretical prediction, a structural evolution diagram for the face-centered-cubic (fcc)-type Aum(SR)n clusters with m up to 92 has been preliminarily established. The structural evolution diagram indicates some basic structural and electronic evolution patterns of thiolate-protected gold nanoclusters. The fcc Aum(SR)n clusters show a genetic structural evolution pattern in which each step of cluster size increase results in the formation of another Au4 tetrahedron or Au3 triangle unit in the Au core, and every increase of a structural unit in the Au core leads to an increase of two electrons in the whole cluster. The unique one- or two-dimensional cluster size evolution, the isomerism of the Au?S framework, and the formation of a double-helical and cyclic tetrahedron network in the fcc Aum(SR)n clusters all can be addressed from this evolution pattern. The summarized cluster structural evolution diagrams enable us to further explore more stable cluster structures and understand their structure?electronic structure?property relationships.
关键词： face-centered-cubic,thiolate-protected gold nanoclusters,density functional theory,electronic structure,structural evolution
更新于2025-09-23 15:19:57
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Screening mixing GW/Bethe–Salpeter approach for triplet states of organic molecules
摘要： We recently proposed a screening mixing many-body ansatz (Ziaei and Bredow 2017 Phys. Rev. B 96 195115) to decrease the typical overestimation of the Hartree–Fock based GW/Bethe–Salpeter equation (BSE) singlet–singlet excitation energies in molecular systems. Now we have evaluated the accuracy of the proposed scheme for triplet states of a set of 20 organic molecules known as the Thiel set. We show that by mixing different screenings into GW and BSE calculated within random phase approximation (in order to ensure best gap and an optimal exciton binding energy), the total mean absolute error of 0.59 eV in the standard Hartree–Fock based eigenvalue GW/BSE approach is reduced to 0.26 eV for 63 triplet states. We further demonstrate that the quasi-particle self-consistent GW/BSE approach in which orbitals and energies are updated in the Green’s function and the dynamically screened interaction mostly and considerably underestimates the excitation energies as shown for a few molecules.
关键词： modified electronic structure method,triplet states,optical properties
更新于2025-09-19 17:15:36
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Calculations of defect states in various sizes of InN nanowires
摘要： InN has received considerable attentions due to its small band-gap and unique properties in the III-nitride family. Understanding the effects of defects on optoelectronic properties of InN nanowire is essential for exploring its applications in future nanodevices. In this work, we have systematically calculated defect states in InN nanowires based on density-functional theory. Hydrogen passivation and several potential intrinsic point defects are considered in various sizes of nanowires, as well as charged defect states. For small-sized hexagonal nanowires, VN at N-poor condition or NIn at N-rich condition is the most stable defect. Whereas for larger-sized nanowires, VN and InN defects are competing when the N chemical potential changes, showing obvious size effect of the defect stability on the nanowire surface. Those defect states change the electronic structure of the nanowires drastically by introducing empty bands or deep level and provide possibility to tailor the optical properties in terms of forming different stable defects.
关键词： InN,nanowires,size effect,first-principals calculations,electronic structure,defects
更新于2025-09-19 17:15:36
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Effect of position and concentration of Li on ZnO physical properties : Density functional investigation
摘要： In this paper, we study the effect of Li position on the physical properties of Li doped ZnO with different concentrations (6.25%,12.5% and 18.75%), by using density functional theory and Boltzmann transport theory. In this work, two possible configurations of Li-doped ZnO are considered : substitution of Zn by Li atom (LiZn), and Li takes the interstitial position (Lii). It is found found that the position and the concentration of Li play an important role in determining the suitable applications for Li doped ZnO. It is also shown that the obtained results are in good agreement with experimental studies.
关键词： Li doped ZnO,Electronic Structure,First principles study,interstitial.,substitution
更新于2025-09-19 17:15:36
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Theoretical study of the structural and electronic properties of impurities in non-passivated silicon thin nanowires
摘要： In this work, we report theoretical results for the presence of the B, C, N, O and F as impurities in non-passivated [001] thin silicon nanowires. The results for the formation energies show that some dopants tend to segregate to the nanowire surfaces, as observed for passivated [110] ones, but at the double negative charge state. The most stable site for the considered impurities is the interstitial one, where the dopants make bridges with the lateral surface Si atoms, below to this surface, except for the oxygen and ?uorine ones, which stay close to the central Si atom. For the neutral carbon, nitrogen and ?uorine impurities, the surface π-states located at the facets are ?lled and a small bandgap appears in the calculated impurity band structures. However, if they were at the double negative charge state, the nanowire metallicity is recovered. Considering the boron and oxygen dopants, the neutral charge state enhances the metallic character at the opposite side of the nanowire where they are, which is reduced when two extra electrons are injected in the system and thus, opening slightly the nanowire bandgap. Our results clearly indicate that doping (or creating vacancies in) these nanowires with acceptors, as well as with hydrogen atoms, can reduce the thin nanowire metallic behavior.
关键词： Electronic structure,Silicon thin nanowires,First row impurities,DFT calculations,Formation energies
更新于2025-09-19 17:15:36
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First Principles Study on Magnetic and Optical Properties of Single Layer CrSi<sub>2</sub>
摘要： According to first-principle based on the density functional theory, the magnetic and optical properties of single layer CrSi2 are calculated and analyzed by plane wave pseudo potential method. The band structure, density of state, optical absorption spectra, reflectivity and energy loss function of single layer CrSi2 are obtained. The results show that single layer CrSi2 has the properties of metal and magnetism. The calculations of optical properties of single layer CrSi2 material deduce that it can absorb photons which belong to visible to ultraviolet region, even in far-infrared and far-ultraviolet regions. Single layer CrSi2 has a good optical permeability to photon (with energy from 13 to 40eV), which shows that single layer CrSi2 is suitable for optoelectronic devices, especially in infrared and vacuum ultraviolet detection applications.
关键词： single layer CrSi2,first-principles,electronic structure,optical properties
更新于2025-09-19 17:15:36
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D-A-π-A based organic dyes for efficient DSSCs: A theoretical study on the role of π-spacer
摘要： A series of novel D-A-π-A organic dyes with different π-spacers for dye-sensitized solar cells (DSSCs) are designed based on hetero-tri-arylamine donor-based dye DP2. The key parameters of all the dyes affecting short-circuit current (JSC) and open-circuit voltage (VOC) are theoretically investigated in detail using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to reveal structure-property relationships. The theoretical results indicate that extending π-spacer is beneficial to improve light-absorbing capacities with larger responsive range of spectra and molar extinction coefficients (ε). The designed dyes DP2-1–DP2-5 exhibit a good balance in various important properties including light harvesting efficiency (LHE), electronic injection driving force (ΔGinject) and vertical dipole moment (μnormal) compared to reference dye DP2. Among all the designed dyes, DP2-3–DP2-5 containing π-spacers with branched chain exhibit obvious red shifted absorption band, smaller regeneration driving force (ΔGreg) and reorganization energy (λtotal), and larger excited state lifetime (τ) and number of photoinjected electrons (nc). This study is expected to provide new clues for the experimental synthesis of highly efficient metal-free organic dyes for DSSCs.
关键词： Electronic structure,Organic dye,Dye-sensitized solar cells,Density functional theory
更新于2025-09-19 17:15:36
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Interplay between Composition, Electronic Structure, Disorder, and Doping due to Dual Sublattice Mixing in Nonequilibrium Synthesis of ZnSnN <sub/>2</sub> :O
摘要： The opportunity for enhanced functional properties in semiconductor solid solutions has attracted vast scientific interest for a variety of novel applications. However, the functional versatility originating from the additional degrees of freedom due to atomic composition and ordering comes along with new challenges in characterization and modeling. Developing predictive synthesis–structure–property relationships is prerequisite for effective materials design strategies. Here, a first-principles based model for property prediction in such complex semiconductor materials is presented. This framework incorporates nonequilibrium synthesis, dopants and defects, and the change of the electronic structure with composition and short range order. This approach is applied to ZnSnN2 (ZTN) which has attracted recent interest for photovoltaics. The unintentional oxygen incorporation and its correlation with the cation stoichiometry leads to the formation of a solid solution with dual sublattice mixing. A nonmonotonic doping behavior as a function of the composition is uncovered. The degenerate doping of near-stoichiometric ZTN, which is detrimental for potential applications, can be lowered into the 1017 cm?3 range in highly off-stoichiometric material, in quantitative agreement with experiments.
关键词： multinary material,computational materials design,disorder,semiconductor solid solution,electronic structure,nonequilibrium synthesis,defects
更新于2025-09-19 17:15:36
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Surface CH <sub/>3</sub> NH <sub/>3</sub><sup>+</sup> to CH <sub/>3</sub><sup>+</sup> Ratio Impacts the Work Function of Solution-Processed and Vacuum-Sublimed CH <sub/>3</sub> NH <sub/>3</sub> PbI <sub/>3</sub> Thin Films
摘要： CH3NH3PbI3 thin films are fabricated using several representative synthesis methods such as spin-coating, evaporation, and a combination of the two. These methods, which frequently occur in reported literatures, use the same precursors PbI2 and CH3NH3I but differ in how the two are mixed. It is found that the latter plays a vital role in determining the surface morphology, composition, and grain size of the films, even when the same stoichiometric ratio of the precursors is used. X-ray photoelectron spectroscopy reveals that the amount of CH3+ -type defects, which results from CH3NH3I dissociation, is sensitive to both the physical state of CH3NH3I and the order of mixing sequence. The variation of the CH3NH3+ ratio also affects the valence band and the work function of the corresponding films, as revealed by ultraviolet photoelectron spectroscopy. Furthermore, the energy-level alignment between the perovskite film and a model hole transport layer, N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine (NPB) is examined. It is found that the CH3NH3+ ratio correlates with the offsets between the valence band maximum of perovskite film and the highest occupied molecular orbital of NPB as well, and the energy-level alignment with the dual-source, coevaporated CH3NH3PbI3 film is most suitable for efficient hole transport.
关键词： electronic structure,methylammonium lead triiodide,solution synthesis,physical evaporation,photoelectron spectroscopy
更新于2025-09-19 17:15:36
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Effect of Net Charge on the Relative Stability of 2D Boron Allotropes
摘要： We study the effect of electron doping on the bonding character and stability of two-dimensional (2D) structures of elemental boron, called borophene, which is known to form many stable allotropes. Our ab initio calculations for the neutral system reveal previously unknown stable 2D ε-B and ω-B structures. We find that the chemical bonding characteristic in this and other boron structures is strongly affected by extra charge. Beyond a critical degree of electron doping, the most stable allotrope changes from ε-B to a buckled honeycomb structure. Additional electron doping, mimicking a transformation of boron to carbon, causes a gradual decrease in the degree of buckling of the honeycomb lattice that can be interpreted as piezoelectric response. Net electron doping can be achieved by placing borophene in direct contact with layered electrides such as Ca2N. We find that electron doping can be doubled by changing from the B/Ca2N bilayer to the Ca2N/B/Ca2N sandwich geometry.
关键词： doping,boron,2D,ab initio calculation,structural stability,electronic structure
更新于2025-09-19 17:15:36