A series of gold clusters spanning the size range from Au6 through Au147 (with diameters from 0.7 to 1.7 nm) in icosahedral, octahedral, and cuboctahedral structure has been theoretically investigated by means of a scalar relativistic all-electron density functional method. One of the main objectives of this work was to analyze the convergence of cluster properties toward the corresponding bulk metal values and to compare the results obtained for the local density approximation (LDA) to those for a generalized gradient approximation (GGA) to the exchange-correlation functional. The average gold–gold distance in the clusters increases with their nuclearity and correlates essentially linearly with the average coordination number in the clusters. An extrapolation to the bulk coordination of 12 yields a gold–gold distance of 289 pm in LDA, very close to the experimental bulk value of 288 pm, while the extrapolated GGA gold–gold distance is 297 pm. The cluster cohesive energy varies linearly with the inverse of the calculated cluster radius, indicating that the surface-to-volume ratio is the primary determinant of the convergence of this quantity toward bulk. The extrapolated LDA binding energy per atom, 4.7 eV, overestimates the experimental bulk value of 3.8 eV, while the GGA value, 3.2 eV, underestimates the experiment by almost the same amount. The calculated ionization potentials and electron affinities of the clusters may be related to the metallic droplet model, although deviations due to the electronic shell structure are noticeable. The GGA extrapolation to bulk values yields 4.8 and 4.9 eV for the ionization potential and the electron affinity, respectively, remarkably close to the experimental polycrystalline work function of bulk gold, 5.1 eV. Gold 4f core level binding energies were calculated for sites with bulk coordination and for different surface sites. The core level shifts for the surface sites are all positive and distinguish among the corner, edge, and face-centered sites; sites in the first subsurface layer show still small positive shifts.

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Here we present the crystal structure, experimental and theoretical characterization of a Au24(SAdm)16 nanomolecule. The composition was verified by X-ray crystallography and mass spectrometry, and its optical and electronic properties were investigated via experiments and first-principles calculations. Most importantly, the focus of this work is to demonstrate how the use of bulky thiolate ligands, such as adamantanethiol, versus the commonly studied phenylethanethiolate ligands leads to a great structural flexibility, where the metal core changes its shape from five-fold to crystalline-like motifs and can adapt to the formation of Au(24±1)(SAdm)16, namely, Au23(SAdm)16, Au24(SAdm)16, and Au25(SAdm)16. The basis for the construction of a thermodynamic phase diagram of Au nanomolecules in terms of ligands and solvent features is also outlined.

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We report the complete X-ray crystallographic structure as determined through single-crystal X-ray diffraction and a thorough theoretical analysis of the green gold Au30(S-tBu)18.\ud While the structure of Au30S(S-tBu)18 with 19 sulfur atoms has been reported, the crystal structure of Au30(S-tBu)18 without the μ3-sulfur has remained elusive until now, though matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS) data unequivocally show its presence in abundance. The Au30(S-tBu)18 nanomolecule not only is distinct in its crystal structure but also has unique temperature-dependent optical properties. Structure determination allows a rigorous comparison and an excellent agreement with theoretical predictions of structure, stability, and optical response

A time-dependent density-functional-theory (TD-DFT) approach is employed to investigate theoretically the optical response of Au nanoclusters of size around N = 150 atoms as a function of: (a) the approximation used for the DFT exchange-correlation (xc-) functional, (b) the shape of the nanocluster. The results of the local-density-approximation (LDA) and the van Leeuwen-Baerends (LB94) xc-functionals are compared on a set of 4 structural motifs: octahedral (N = 146), cuboctahedral (N = 147), icosahedral (N = 147), and cubic (N = 172), representative of both crystalline and noncrystalline motifs commonly encountered in the study of metal nanoclusters. It is found that the position of the peak in the photoabsorption spectrum is weakly dependent on the shape of the cluster but is strictly related to its size and to the DFT xc-functional used in the calculations, with the finding that the predictions of the LB94 xc-functional compare better with the available experimental data on the absorption spectrum of Au particles in this size range with respect to those of the LDA xc-functional. The detailed shape of the cluster becomes apparent in the form of the absorption spectrum, which can be symmetric or asymmetric in two different forms.

We report a detailed study on the optical properties of Au(SR) using steady-state and transient absorption measurements to probe its metallic nature, time-dependent density functional theory (TDDFT) studies to correlate the optical spectra, and density of states (DOS) to reveal the factors governing the origin of the collective surface plasmon resonance (SPR) oscillation. Au is the smallest identified gold nanocrystal to exhibit SPR. Its optical absorption exhibits SPR at 510 nm. Power-dependent bleach recovery kinetics of Au suggests that electron dynamics dominates its relaxation and it can support plasmon oscillations. Interestingly, TDDFT and DOS studies with different tail group residues (-CH and -Ph) revealed the important role played by the tail groups of ligands in collective oscillation. Also, steady-state and time-resolved absorption for Au, Au, and Au were studied to reveal the molecule-to-metal evolution of aromatic AuNMs. The optical gap and transient decay lifetimes decrease as the size increases.

Articles you may be interested inA new algorithm to solve the Time Dependent Density Functional Theory (TDDFT) equations in the space of the density fitting auxiliary basis set has been developed and implemented. The method extracts the spectrum from the imaginary part of the polarizability at any given photon energy, avoiding the bottleneck of Davidson diagonalization. The original idea which made the present scheme very efficient consists in the simplification of the double sum over occupied-virtual pairs in the definition of the dielectric susceptibility, allowing an easy calculation of such matrix as a linear combination of constant matrices with photon energy dependent coefficients. The method has been applied to very different systems in nature and size (from H 2 to [Au 147 ] − ). In all cases, the maximum deviations found for the excitation energies with respect to the Amsterdam density functional code are below 0.2 eV. The new algorithm has the merit not only to calculate the spectrum at whichever photon energy but also to allow a deep analysis of the results, in terms of transition contribution maps, Jacob plasmon scaling factor, and induced density analysis, which have been all implemented. C 2015 AIP Publishing LLC. [http://dx