Density functional investigation of the adsorption effects of PH3 and SH2 on the structure stability of the Au-55 and Pt-55 nanoclusters

Author(s)

Guedes-Sobrinho, Diego ; Chaves, Anderson S. ; Piotrowski, Mauricio J. ; Da Silva, Juarez L. F.

• Document type: Journal article
• Source: Journal of Chemical Physics; v. 146, n. 16 APR 28 2017.
• Web of Science Citations: 3

Abstract

Although several studies have been reported for Pt-55 and Au-55 nanoclusters, our atomistic understanding of the interplay between the adsorbate-surface interactions and the mechanisms that lead to the formation of the distorted reduced core (DRC) structures, instead of the icosahedron (ICO) structure in gas phase, is still far from satisfactory. Here, we report a density functional theory (DFT) investigation of the role of the adsorption effects of PH3 (one lone pair of electrons) and SH2 (two lone pairs) on the relative stability of the Pt-55 and Au-55 nanoclusters. In gas phase, we found that the DRC structures with 7 and 9 atoms in the core region are about 5.34 eV (Pt-55) and 2.20 eV (Au-55) lower in energy than the ICO model with I-h symmetry and 13 atoms in the core region. However, the stability of the ICO structure increases by increasing the number of adsorbed molecules from 1 to 18, in which both DRC and ICO structures are nearly degenerate in energy at the limit of 18 ligands, which can be explained as follows. In gas phase, there is a strong compression of the cationic core region by the anionic surface atoms induced by the attractive Coulomb interactions (core(+)-surface(-)), and hence, the strain release is obtained by reducing the number of atoms in the cationic core region, which leads to the 55 atoms distorted reduced core structures. Thus, the Coulomb interactions between the core(+) and surface(-) contribute to break the symmetry in the ICO55 structure. On the other hand, the addition of ligands on the anionic surface reduces the charge transfer between the core and surface, which contributes to decrease the Coulomb interactions and the strain on the core region of the ICO structure, and hence, it stabilizes a compact ICO structure. The same conclusion is obtained by adding van der Waals corrections to the plain DFT calculations. Similar results are obtained by the addition of steric effects, which are considered through the adsorption of triphenylphosphine (PPh3) molecules on Au-55, in which the relative stability between ICO and DRC is the same as for PH3 and SH2. However, for Pt-55, we found an inversion of stability due to the PPh3 ligand effects, where ICO has higher stability than DRC by 2.40 eV. Our insights are supported by several structural, electronic, and energetic analyses. Published by AIP Publishing. (AU)

• FAPESP's process: 13/15112-9 - Ab initio study of the effects of ligands on the atomic structure, electronic stability and transition metal nanoclusters
• Grantee: Diêgo Guedes Sobrinho
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 13/21045-2 - Theoretical prediction of the structure, thermodynamic stability, electronic, and reactivity properties of nanoclusters
• Grantee: Juarez Lopes Ferreira da Silva
• Support Opportunities: Regular Research Grants