Evidencing the relationship between isomer spectra and melting: the 20- and 55-atom silver and gold cluster cases

Abstract

The present work highlights the links between melting properties and structural excitation spectra of small gold and silver clusters.

Density-functional tight-binding: basic concepts and applications to molecules and clusters

“…Other DFTB thermodynamical studies were concerned with metallic systems and in particular silver and gold clusters. The effect of charge on the doubly magic (electronically closed shell and geometrically a symmetric pyramid) cluster Au 20 was investigated [359] as well as the the correlation between the isomer spectra features and the nature of the solid-to-liquid transition [360], from the comparison between the caloric curves of structurally ordered systems (Au 20 , Ag 55 ) and those of disordered cases (Ag 20 , Au 55 ).…”

Exploring energy landscapes at the DFTB quantum level using the threshold algorithm: the case of the anionic metal cluster Au$$_{20}^{-}$$

“…The DFTB parameters used were adapted [112,116,124] from those reported by Fihey et al [111] (the "auorg" set from the www.dftb.org website). The modification consisted in a shift of the p orbital energy [112].…”

“…The simulation protocol was initiated using as starting structures the 10 isomers reported as the lowest energy ones in the references [115,116]. Additional isomers identified during an iteration of the DFTB/threshold scheme were added to the list of starting structures if they met one of the two following criteria: i/ a total energy differing from the one of the pyramid, assumed to be the global minimum, by less than 0.45 eV or ii/ that a given minimum j represents more than 10% of the optimized structures issued from a given starting configuration i at a given lid (p i→j > 10%).…”

“…Among the vast literature focused on gold clusters , numerous works are devoted to Au 20 [63,64,66,73,74,80,88,99,107] because this cluster presents a double magic number: its atomic structure is a highly symmetrical pyramid and, in the simple spherical Jellium model, its 20-electron outer electronic shell is closed (1s 2 1p 6 1d 10 2s 2 superorbital configuration). In recent studies, employing a new adaptation of DFTB parameters [109,111,112], we have investigated the potential energy surface (PES) of Au (0,+,−) 20 by combining a Parallel Tempering Molecular Dynamics (PTMD) exploration [113] with periodic quenching to obtain isomers and compute their structural excitation and vibrational spectra [114][115][116]. We have observed that the Au (0,+,−) 20 lowest energy isomers exhibit pyramidal shapes, highly symmetric (T d ) for the neutral one and with very small Jahn-Teller deformations from the T d symmetry for the ions [114][115][116].…”

“…In recent studies, employing a new adaptation of DFTB parameters [109,111,112], we have investigated the potential energy surface (PES) of Au (0,+,−) 20 by combining a Parallel Tempering Molecular Dynamics (PTMD) exploration [113] with periodic quenching to obtain isomers and compute their structural excitation and vibrational spectra [114][115][116]. We have observed that the Au (0,+,−) 20 lowest energy isomers exhibit pyramidal shapes, highly symmetric (T d ) for the neutral one and with very small Jahn-Teller deformations from the T d symmetry for the ions [114][115][116]. These findings are in agreement with the literature, both experimental (IR [63], Trapped Ion Electron Diffraction [117], ion mobility [118] and atomic imaging [119]) and theoretical [63,120].…”