Centre d’Élaboration de Matériaux et d’Etudes Structurales


Accueil > Recherche > SINanO : Surfaces, Interfaces et Nano-Objets > Thématiques de Recherche

Nano-objects : properties

Selection of our most recent publications on this topic (from 2018) - The names of the team members are in blue


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

 

Mathias Rapacioli, Fernand Spiegelman and Nathalie Tarrat

Phys. Chem. Chem. Phys., 2019,21, 24857-24866

 

The present work highlights the links between melting properties and structural excitation spectra of small gold and silver clusters. The heat capacity curves are computed for Ag20, Au20, Ag55, Au55 and their ions, using a parallel-tempering molecular dynamics scheme to explore the density functional based tight binding (DFTB) potential energy surfaces and the multiple histogram method. It is found that clusters having very symmetric lowest energy structures (Au20, Ag55 and their ions) present sharp or relatively sharp solid-to-liquid transitions and large melting temperatures, important structural excitation energies and a discrete isomer spectrum. Opposite trends are observed for less ordered clusters (Ag20, Au55 and their ions). Regarding the structural evolution with temperature, very symmetric clusters exhibit minor evolution up to the starting melting temperature. The present study also highlights that, in contrast with the case of Au20, a single electron excess or deficiency is not determinant regarding the melting characteristics, even quantitatively, for clusters containing 55 atoms, for gold as for silver.

 


Melting of the Au20 Gold Cluster : Does Charge Matter ?

 

Mathias Rapacioli, Nathalie Tarrat, Fernand Spiegelman

J. Phys. Chem. A 2018, 122, 16, 4092–4098

 

 

We investigate the dependence upon the charge of the heat capacities of magic gold cluster Au20 obtained from density functional-based tight binding theory within parallel tempering molecular dynamics and the multiple histogram method. The melting temperatures, determined from the heat capacity curves, are found to be 1102 K for neutral Au20 and only 866 and 826 K for Au20+ and Au20. Both the canonical and the microcanonical aspects of the transition are discussed. A convex intruder, associated with a negative heat capacity, is evidenced in the microcanonical entropy in the case of the neutral cluster but is absent in the melting processes of the ions. The present work shows that a single charge quantitatively affects the thermal properties of the gold 20mer.