LABORATORY OF MOLECULAR STRUCTURES AND MODELING

BABES-BOLYAI UNIVERSITY

The scientific activities for partner P4 in the first stage of the project involve the assessment of the gold nanoparticles-functional group interactions at a computational level. Thus, we have been interested in estimating the interaction of gold atoms with functional groups such as thiolates and correlating the theoretical results to experimental ones. The study was carried using DFT methods, but several functionals and basis sets are employed and analyzed, in order to find one that best suits the considered species.

So far, two approaches were taken. One is approximating the surface of a gold nanoparticle with a planar arrangement of four gold atoms, in initial D_4d symmetry. This is then functionalized with 2 or 4 groups of the type RS^-, RSe^-, RO^- (see Figure 1, R=Me, Ph). The geometrical parameters, vibrational spectra and HOMO-LUMO gaps are calculated for the optimized structures. The HOMO-LUMO gap is of particular interest in this stage, as it can hint to the stability of the species and thus the best group which can be used in functionalizing the gold surface.

Figure 1. Optimized BP86 geometry of Au₄(SeMe)₂

The other approach involves estimating the gold nanoparticles through clusters of various sizes. So far, Au₁₂ clusters have been built and based on published data, the best symmetry of such molecules is found to be a C_2v one (Figure 2), rather than the more symmetrical icosahedronal geometry. The stabilization of such clusters by functionalization with thiolate groups is reflected in the HOMO-LUMO gap that can be estimated through theoretical calculations. Also, the number of organic groups on the surface of the cluster is believed to play an important role.

Figure 2. Optimized BP86 geometry of the Au₁₂ cluster

Main activities:

Design and modeling of supra-molecular structures.

Theory and experiments for surface chemistry.

Basis equipments:

Cluster composed from 24 PCs (equiped with dedicated software for high level quantum chemical calculations).

Computer cluster – 70 state of the art processors,

PC network