Uma comparação teórica das propriedades estruturais e espectroscópicas de pequenos clusters bimetálicos e monocomponentes de prata, ouro e cobre

Abstract

Computational design has been increasingly employed in the rational development of new materials with highly targeted properties for multifunctional applications, i.e., due to the optimization of properties in an extremely short time to obtain results. Small bimetallic clusters (atoms / molecules) of noble metals, in particular, and their single components have been the focus of numerous studies in various fields of technological application. Despite the recognized great importance of these materials, however, there is a consensus that much of their properties are not yet very well understood microscopically. Thus, the present work presents a detailed theoretical analysis of small bimetallic clusters and single-components of silver (𝐴𝑔), gold (𝐴𝑢), copper (𝐶𝑢) and their combinations. For this purpose, the Kohn-Sham density functional theory and time dependent density functional theory calculations were employed using the functional BP86 with the LANL2DZ base set, as implemented in the ORCA code 4.0. Theoretical results showed that, in the Mulliken population analysis, the presence of charge distributions and defined polarities between the atoms of some clusters indicated interaction potentials to polarized ligands. The energy gap analysis from the LUMO-HOMO energies difference showed an oscillation of their values as the cluster size and geometry is changed. For the decamers (10-atom clusters) of 𝐴𝑔, 𝐴𝑢 and 𝐶𝑢, a significant change in the UV-vis absorbance spectrum for ionic and neutral clusters can be observed. This is because the presence of positive / negative charge modifies the structural properties of clusters, such as the mean bond length (𝑑𝑎𝑣𝑔). Similarly, a subtle change in UV-vis spectra in different solvents was visualized in good agreement with the literature. These small changes were attributed due to the symmetry of the clusters, uniformity in the distribution of the constituent atoms and possibly also the polarity of the solvents used and how this alters the 𝑑𝑎𝑣𝑔 between atoms in the cluster. Moreover, such structural changes cause different types of distortions, that is, for 𝐴𝑔 and 𝐴𝑢 clusters our data suggest that these distortions are more symmetrical, whereas in the case of Cu we can observe a more asymmetric cluster distortion. Therefore, these results are employed to elucidate the effects of size, geometry and composition, on the electronic structure and spectroscopic properties of these bimetallic clusters.