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Guidez, Emilie B.

Publications and source records attributed to Guidez, Emilie B..

4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Theoretical Investigation of Relaxation Dynamics in Au 38 (SH) 24 Thiolate-Protected Gold Nanoclusters

A subtle change in the electronic structure of thiolate protected noble nanoparticles can result distinctive relaxation dynamics. Thus, relaxation dynamics investigations on different sizes and structures of thiolate protected gold nanocluster will reveal their physical and chemical properties for further development of catalytic applications. In this work, we performed nonradiative relaxation dynamics of the Au 38 (SH) 24 nanocluster theoretically to describe electron relaxation dynamics. The core and higher excited states involving semiring motifs lying in the energy range 0.00-2.01 eV are investigated using the time-dependent density functional theory (TDDFT). The surface hopping method with decoherence correction, augmented with a real-time approach to DFT technique is used to assess the quantum dynamics. The Au 23 core relaxations were found to be in a picosecond timescale in the range of 2.0 – 8.2 ps. The higher excited states that consist of core- semiring mixed or semiring states gave ultrafast decay time constants in the range of 0.6 - 4.9 ps. Our calculations predicted that the slowest individual state decay of S11 or the slowest combined S 11 -S 12 , S 1 -S 2 -S 6 -S 7 and S 4 -S 5 - S 9 -S 10 decay involves intracore relaxations. The analysis of the phonon spectral densities and the ground state vibrational frequencies suggested that the low frequency (25 cm -1 ) coherent phonon emission reported experimentally could be the bending of the biicosahedral Au 23 core or the “fan blade twisting” mode of two icosahedral units occurring in a similar frequency range.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Perspective: Ab initio force field methods derived from quantum mechanics

It is often desirable to accurately and efficiently model the behavior of large molecular systems in the condensed phase (thousands to tens of thousands of atoms) over long time scales (from nanoseconds to milliseconds). In these cases, ab initio methods are difficult due to the increasing computational cost with the number of electrons. A more computationally attractive alternative is to perform the simulations at the atomic level using a parameterized function to model the electronic energy. Many empirical force fields have been developed for this purpose. However, the functions that are used to model interatomic and intermolecular interactions contain many fitted parameters obtained from selected model systems, and such classical force fields cannot properly simulate important electronic effects. Furthermore, while such force fields are computationally affordable, they are not reliable when applied to systems that differ significantly from those used in their parameterization. They also cannot provide the information necessary to analyze the interactions that occur in the system, making the systematic improvement of the functional forms that are used difficult. Ab initio force field methods aim to combine the merits of both types of methods. The ideal ab initio force fields are built on first principles and require no fitted parameters. Ab initio force field methods surveyed in this perspective are based on fragmentation approaches and intermolecular perturbation theory. This perspective summarizes their theoretical foundation, key components in their formulation, and discusses key aspects of these methods such as accuracy and formal computational cost. The ab initio force fields considered here were developed for different targets, and this perspective also aims to provide a balanced presentation of their strengths and shortcomings. Finally, this perspective suggests some future directions for this actively developing area.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Quantum coherent plasmon in silver nanowires: A real-time TDDFT study

A plasmon-like phenomenon, arising from coinciding resonant excitations of different electronic characteristics in 1D silver nanowires, has been proposed based on theoretical linear absorption spectra. Such a molecular plasmon holds the potential for anisotropic nanoplasmonic applications. However, its dynamical nature remains unexplored. In this work, quantum dynamics of longitudinal and transverse excitations in 1D silver nanowires are carried out within the real-time time-dependent density functional theory framework. The anisotropic electron dynamics confirm that the transverse transitions of different electronic characteristics are collective in nature and oscillate in-phase with respect to each other. Analysis of the time evolutions of participating one-electron wave functions suggests that the transverse transitions form a coherent wave packet that gives rise to a strong plasmon resonance at the molecular level.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗