5 research outputs found

    Extension of the Time-Dependent Density Functional Complex Polarizability Algorithm to Circular Dichroism: Implementation and Applications to Ag<sub>8</sub> and Au<sub>38</sub>(SC<sub>2</sub>H<sub>4</sub>C<sub>6</sub>H<sub>5</sub>)<sub>24</sub>

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    We detail the calculation of rotatory strengths as an extension of the complex polarizability algorithm of time dependent density functional theory (TDDFT) proposed in a recent publication (O. Baseggio, G. Fronzoni, M. Stener, <i>J. Chem. Phys.</i> <b>2015</b>, <i>143</i>, 024106). To demonstrate the generality and applicability of the proposed algorithm, we calculate the photoabsorption and circular dichroism (CD) spectra of Ag<sub>8</sub> (as a validation case), Au<sub>38</sub>(SCH<sub>3</sub>)<sub>24</sub>, and Au<sub>38</sub>(SCH<sub>2</sub>CH<sub>2</sub>Ph)<sub>24</sub> monolayer-protected gold clusters (as a system of great current interest for their optical properties). For Au<sub>38</sub>(SCH<sub>2</sub>CH<sub>2</sub>Ph)<sub>24</sub>, the computed CD spectrum agrees well with the experimental data from the literature. Furthermore, a comparison of the calculated CD spectra of the two thiolate-protected nanoclusters reveals that the most distinctive features of the spectra are rather insensitive to the nature of the thiolate tail groups, which, however, play a significant role in shaping optical and dichroic response of the systems, especially in the higher energy portion of the spectrum

    Photoabsorption of Icosahedral Noble Metal Clusters: An Efficient TDDFT Approach to Large-Scale Systems

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    7noWe apply a recently developed time-dependent density functional theory (TDDFT) algorithm based on the complex dynamical polarizability to calculate the photoabsorption spectrum of the following series of closed-shell icosahedral clusters of increasing size (namely, [M13]5+, [M55]3−, [M147]−, and [M309]3+ with M = Ag, Au), focusing in particular on their plasmonic response. The new method is shown to be computationally very efficient: it simultaneously retains information on the excited-state wave function and provides a detailed analysis of the optical resonances, e.g., by employing the transition contribution map scheme. For silver clusters, a very intense plasmon resonance is found for [Ag55]3−, with strong coupling among low-energy single-particle configurations. At variance, for gold clusters we do not find a single strong plasmonic peak but rather many features of comparable intensity, with partial plasmonic behavior present only for the lowest-energy transitions. Notably, we also find a much greater sensitivity of the optical response of Ag clusters with respect to Au clusters to cluster charge, the exchange-correlation (xc) functional, and the basis set, as demonstrated via a detailed comparison between [Ag55]q and [Au55]q. The results of the TDDFT algorithm obtained with the complex dynamical polarizability are finally compared with those produced by alternative (real-time evolution or Lanczos) approaches, showing that, upon proper choice of numerical parameters, overall nearly quantitative agreement is achieved among all of the considered approaches, in keeping with their fundamental equivalence.partially_openopenBaseggio, Oscar; De Vetta, Martina; Fronzoni, Giovanna; Stener, Mauro; Sementa, Luca; Fortunelli, Alessandro; Calzolari, ArrigoBaseggio, Oscar; De Vetta, Martina; Fronzoni, Giovanna; Stener, Mauro; Sementa, Luca; Fortunelli, Alessandro; Calzolari, Arrig

    Fe L‑Edge X‑ray Absorption Spectra of Fe(II) Polypyridyl Spin Crossover Complexes from Time-Dependent Density Functional Theory

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    L-edge near-edge X-ray fine structure spectroscopy (NEXAFS) has become a powerful tool to study the electronic structure and dynamics of metallo-organic and biological compounds in solution. Here, we present a series of density functional theory calculations of Fe L-edge NEXAFS for spin crossover (SCO) complexes within the time-dependent framework. Several key factors that control the L-edge excitations have been carefully examined using an Fe­(II) polypyridyl complex [Fe­(tren­(py)<sub>3</sub>)]<sup>2+</sup> (where tren­(py)<sub>3</sub> = tris­(2-pyridylmethyliminoethyl)­amine) as a model system. It is found that the electronic spectra of the low-spin (LS, singlet), intermediate-spin (IS, triplet), and high-spin (HS, quintet) states have distinct profiles. The relative energy positions, but not the spectral profiles, of different spin states are sensitive to the choice of the functionals. The inclusion of the vibronic coupling leads to almost no visible change in the resulting NEXAFS spectra because it is governed only by low-frequency modes of less than 500 cm<sup>–1</sup>. With the help of the molecular dynamics sampling in acetonitrile at 300 K, our calculations reveal that the thermal motion can lead to a noticeable broadening of the spectra. The main peak position is strongly associated with the length of the Fe–N bond

    Computational Study of Amino Mediated Molecular Interaction Evidenced in N 1s NEXAFS: 1,4-Diaminobenzene on Au (111)

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    Primary amines can interact with neighbor molecules or with a metal substrate via weak bonds involving the electron lone pair of their amino functional group. Near edge X-ray absorption spectra (NEXAFS) on the N 1s edge show that the structure of the empty molecular orbitals localized on the nitrogen atom is very sensitive to these interactions. Here we investigate the origin of these changes by means of theoretical calculations. NEXAFS spectra are simulated for the 1,4-benzenediamine (BDA) molecule in its free, crystalline, and monolayer on Au(111) forms. We identify the electronic states which are affected by these amino-based interactions. In the case of the molecular layer grown on the gold substrate, we show how the results of the calculations can be used to identify intermolecular interactions influencing adsorption geometries in molecular monolayers

    Chemistry of the Methylamine Termination at a Gold Surface: From Autorecognition to Condensation

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    13The self-assembly of the naphthylmethylamine molecules (NMA) on the Au(111) surface is investigated by a combined experimental and theoretical approach. Three well-defined phases are observed upon different thermal treatments at the monolayer stage. The role played by the methylamine termination is evidenced in both the molecule–molecule and molecule–substrate interactions. The autorecognition process of the amino groups is identified as the driving factor for the formation of a complex hydrogen bonding scheme in small molecular clusters, possibly acting also as a precursor of a denitrogenation condensation process induced by thermal annealing.reservedmixedDri, Carlo; Fronzoni, Giovanna; Balducci, Gabriele; Furlan, Sara; Stener, Mauro; Feng, Zhijing; Comelli, Giovanni; Castellarin-Cudia, Carla; Cvetko, Dean; Kladnik, Gregor; Verdini, Alberto; Floreano, Luca; Cossaro, AlbanoDri, Carlo; Fronzoni, Giovanna; Balducci, Gabriele; Furlan, Sara; Stener, Mauro; Feng, Zhijing; Comelli, Giovanni; Castellarin Cudia, Carla; Cvetko, Dean; Kladnik, Gregor; Verdini, Alberto; Floreano, Luca; Cossaro, Alban