148 research outputs found
Efficient approach for simulating distorted materials
The operation principles of nanoscale devices are based upon both electronic
and mechanical properties of materials. Because these properties can be
coupled, they need to be investigated simultaneously. At this moment, however,
the electronic structure calculations with custom-made long-range mechanical
distortions are impossible, or expensive at best. Here we present a unified
formalism to solve exactly the electronic structures of nanomaterials with
versatile distortions. We illustrate the formalism by investigating twisted
armchair graphene nanoribbons with the least possible number of atoms. Apart
from enabling versatile material distortions, the formalism is capable of
reducing computational costs orders of magnitude in various areas of science
and engineering.Comment: 4 pages, 2 figures, 2 table
Self-passivating edge reconstructions of graphene
Planar reconstruction patterns at the zigzag and armchair edges of graphene
were investigated with density functional theory. It was unexpectedly found
that the zigzag edge is metastable and a planar reconstruction spontaneously
takes place at room temperature. The reconstruction changes electronic
structure and self-passivates the edge with respect to adsorption of atomic
hydrogen from molecular atmosphere.Comment: 4 pages, 4 figures, 1 tabl
Point Group Symmetry Analysis of the Electronic Structure of Bare and Protected Metal Nanocrystals
The electronic structures of a variety of experimentally identified gold and
silver nanoclusters from 20 to 246 atoms, either unprotected or protected by
several types of ligands, are characterized by using point group specific
symmetry analysis. The delocalized electron states around the HOMO-LUMO energy
gap, originating from the metal s-electrons in the cluster core, show symmetry
characteristics according to the point group that describes best the atomic
arrangement of the core. This indicates strong effects of the lattice structure
and overall shape of the metal core to the electronic structure, which cannot
be captured by the conventional analysis based on identification of spherical
angular momentum shells in the superatom model. The symmetry analysis discussed
in this paper is free from any restrictions regarding shape or structure of the
metal core, and is shown to be superior to the conventional spherical harmonics
analysis for any symmetry that is lower than Ih. As an immediate application,
we also demonstrate that it is possible to reach considerable savings in
computational time by using the symmetry information inside a conventional
linear-response calculation for the optical absorption spectrum of the Ag55
cluster anion, without any loss in accuracy of the computed spectrum. Our work
demonstrates an efficient way to analyze the electronic structure of
non-spherical, but atomically ordered nanocrystals and ligand-protected
clusters with nanocrystal metal cores and it can be viewed as the
generalization of the superatom model demonstrated for spherical shapes ten
years ago (Walter et al., PNAS 2008, 105, 9157)
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Gold–Thiolate Nanocluster Dynamics and Intercluster Reactions Enabled by a Machine Learned Interatomic Potential
Monolayer protected metal clusters comprise a rich class of molecular systems and are promising candidate materials for a variety of applications. While a growing number of protected nanoclusters have been synthesized and characterized in crystalline forms, their dynamical behavior in solution, including prenucleation cluster formation, is not well understood due to limitations both in characterization and first-principles modeling techniques. Recent advancements in machine-learned interatomic potentials are rapidly enabling the study of complex interactions such as dynamical behavior and reactivity on the nanoscale. Here, we develop an Au-S-C-H atomic cluster expansion (ACE) interatomic potential for efficient and accurate molecular dynamics simulations of thiolate-protected gold nanoclusters (Aun(SCH3)m). Trained on more than 30,000 density functional theory calculations of gold nanoclusters, the interatomic potential exhibits ab initio level accuracy in energies and forces and replicates nanocluster dynamics including thermal vibration and chiral inversion. Long dynamics simulations (up to 0.1 μs time scale) reveal a mechanism explaining the thermal instability of neutral Au25(SR)18 clusters. Specifically, we observe multiple stages of isomerization of the Au25(SR)18 cluster, including a chiral isomer. Additionally, we simulate coalescence of two Au25(SR)18 clusters and observe series of clusters where the formation mechanisms are critically mediated by ligand exchange in the form of [Au-S]n rings
Directing Intrinsic Chirality in Gold Nanoclusters: Preferential Formation of Stable Enantiopure Clusters in High Yield and Experimentally Unveiling the “Super” Chirality of Au
Chiral gold nanoclusters offer significant potential for exploring chirality at a fundamental level and for exploiting their applications in sensing and catalysis. However, their widespread use is impeded by low yields in synthesis, tedious separation procedures of their enantiomeric forms, and limited thermal stability. In this study, we investigated the direct synthesis of enantiopure chiral nanoclusters using the chiral ligand 2-MeBuSH in the fabrication of Au, Au, and Au nanoclusters. Notably, this approach leads to the unexpected formation of intrinsically chiral clusters with high yields for chiral Au and Au nanoclusters. Experimental evaluation of chiral activity by circular dichroism (CD) spectroscopy corroborates previous theoretical calculations, highlighting the stronger CD signal exhibited by Au compared to Au or Au. Furthermore, the formation of a single enantiomeric form is experimentally confirmed by comparing it with intrinsically chiral Au(2-PET) (2-PET: 2-phenylethanethiol) and is supported theoretically for both Au and Au. Moreover, the prepared chiral clusters show stability against diastereoisomerization, up to temperatures of 80°C. Thus, our findings not only demonstrate the selective preparation of enantiopure, intrinsically chiral, and highly stable thiolate-protected Au nanoclusters through careful ligand design but also support the predicted “super” chirality in the Au cluster, encompassing hierarchical chirality in ligands, staple configuration, and core structure
Real-space imaging with pattern recognition of a ligand-protected Ag374 nanocluster at sub-molecular resolution
厦门大学化学化工学院郑南峰教授团队长期致力于研究固体功能材料的表界面化学行为,在分子水平上实现对固体功能材料的化学性能的调控与优化。得益于固体表面物理化学国家重点实验室的多学科合作以及能源材料化学协同创新中心的多单位优势互补,郑南峰教授课题组通过与校内外多个课题组的密切合作,近期在功能材料的可控制备、复杂表界面结构的高分辨表征和表界面过程分子机制的深入理解等方面取得系列重要进展,相关成果近期均在Nature Communications发表。
针对纳米颗粒表面配体难被高分辨直接成像的特点,与厦门大学郑兰荪、谢兆雄等教授以及中科院大连化物所杨学明研究员、马志博副研究员和芬兰于韦斯屈莱大学HannuHäkkinen教授等多个团队紧密合作,在利用扫描隧道显微镜表征金属纳米团簇的表面配体层结构方面取得重要进展。以原子结构精确的 Ag374纳米团簇为研究对象,利用超高真空扫描隧道显微镜分别在液氦及液氮温度下获得了单个团簇亚分子高分辨率的拓扑图像。【Abstract】High-resolution real-space imaging of nanoparticle surfaces is desirable for better understanding of surface composition and morphology, molecular interactions at the surface, and nanoparticle chemical functionality in its environment. However, achieving molecular or sub-molecular resolution has proven to be very challenging, due to highly curved nanoparticle surfaces and often insufficient knowledge of the monolayer composition. Here, we demonstrate sub-molecular resolution in scanning tunneling microscopy imaging of thiol monolayer of a 5 nm nanoparticle Ag374 protected by tert-butyl benzene thiol. The experimental data is confirmed by comparisons through a pattern recognition algorithm to simulated topography images from density functional theory using the known total structure of the Ag374 nanocluster. Our work demonstrates a working methodology for investigations of structure and composition of organic monolayers on curved nanoparticle surfaces, which helps designing functionalities for nanoparticle-based applications.The experimental work done in Dalian Institute of Chemical Physics (DICP),
Chinese Academy of Sciences, was supported both by Xiamen University (The
National Key R&D Program of China grant 2017YFA0207302, National Natural
Science Foundation of China, grant 21731005, 21420102001 and 21721001 the
National Key R&D Program of China grant 2017YFA0207302) and DICP (National
Natural Science Foundation of China grant 21688102, the Strategic Priority Research
Program of Chinese Academy of Science, grant XDB17000000, the National Key
Research and Development Program of the MOST of China, grant 2016YFA0200603
and the open fund of the state key laboratory of molecular reaction dynamics in DICP,
CAS, grant SKLMRD-K201707). Q.Z. thanks Dr. Huayan Yang for providing the samples
for STM imaging. S.M. and H.H. thank T. Kärkkäinen and P. Nieminen for discussions
on pattern recognition algorithms. The theoretical and computational work in the
University of Jyväskylä was funded by the Academy of Finland (grants 294217, 315549,
AIPSE program, and H.H.’s Academy Professorship). H.H. acknowledges the support
from China’s National Innovation and Intelligence Introduction Base visitor program.
S.K. thanks the Vilho, Yrjö, and Kalle Väisälä Foundation for the grant for doctoral
studies. The DFT simulations were done at the Finnish national supercomputing center
CSC and at the Barcelona Supercomputing Center (PRACE project “NANOMETALS”).
研究工作得到了科技部、国家自然科学基金委和教育部,中科院先导项目,国家重点研发计划,分子反应动力学国家重点实验室开放课题基金等项目的资助
All-thiol-stabilized Ag44 and Au12Ag32 nanoparticles with single-crystal structures
该研究工作是在厦门大学郑南峰教授课题组和芬兰于韦斯屈莱大学Hannu Häkkinen课题组共同合作完成的。工作中的合成、结构表征和性能测试是在郑南峰教授指导下由博士生杨华艳(第一作者)和硕士生王羽、黄华奇完成的;Hannu Häkkinen课题组通过理论计算分析了Ag44的电子结构和吸收光谱。Noble metal nanoparticles stabilized by organic ligands are important for applications in assembly, site-specific bioconjugate labelling and sensing, drug delivery and medical therapy, molecular recognition and molecular electronics, and catalysis. Here we report crystal structures and theoretical analysis of three Ag44(SR)30 and three Au12Ag32(SR)30 intermetallic nanoclusters stabilized with fluorinated arylthiols (SR=SPhF, SPhF2 or SPhCF3). The nanocluster forms a Keplerate solid of concentric icosahedral and dodecahedral atom shells, protected by six Ag2(SR)5 units. Positive counterions in the crystal indicate a high negative charge of 4− per nanoparticle, and density functional theory calculations explain the stability as an 18-electron superatom shell closure in the metal core. Highly featured optical absorption spectra in the ultraviolet–visible region are analysed using time-dependent density functional perturbation theory. This work forms a basis for further understanding, engineering and controlling of stability as well as electronic and optical properties of these novel nanomaterials.国家自然科学基金(项目批准号:21131005, 21021061, 20925103)、科技部(项目批准号:2011CB932403, 2009CB930703)和芬兰科学院基
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