RESUMO
A theoretical study has been performed for deposited AumAgn (m + n = 1-6) clusters. The combined use of the Mexican Enhanced Genetic Algorithm (MEGA) and Density Functional Theory (DFT) calculations allows us to explore the potential energy surface and therefore, find the global minimum configuration for each composition. We have performed calculations of clusters deposited on defects (oxygen vacancies) known as F centers on MgO (100) surfaces. Our results show interesting differences in the geometries of the clusters upon deposition and as a consequence in their electronic properties. The combination of two metals with different electronegativities creates an inhomogeneous charge distribution on their exposed surface producing good conditions for a catalytic process to take place.
RESUMO
A comparative theoretical study has been performed of the gas phase and deposited AumRhn (4 ≤ m + n ≤ 6) clusters. The combined use of a genetic algorithm and Density Functional Theory (DFT) calculations allows us to explore the potential energy surface and, therefore, find efficiently and automatically the global minimum configuration for each composition. Our results show interesting effects on the geometries of the clusters on deposition. This occurs because the rhodium atoms (electronically) prefer to be in contact with the MgO surface, sometimes promoting planar clusters to become three-dimensional when deposited, and three-dimensional clusters in the gas phase to become two-dimensional. Together with the change in geometries, the magnetic moment is reduced from the gas phase, as the electrons rearrange themselves when the cluster interacts with the substrate.
RESUMO
Anion photoelectron spectroscopy (PES) and ab initio calculations have been used to identify the unique structural, electronic, and magnetic properties of both neutral and anionic binary AunRhm (n = 1-7 and m = 1-2) clusters in vacuo. Negative ion photoelectron spectra are presented with electron binding energies measured up to 3.493 eV. We discuss our computational results in the context of the PES experiment, in which the calculated electron affinities and vertical detachment energies are in good agreement with the measured values. Theoretically, we investigate the low-lying energy structures and the spin isomers of each neutral, anionic and cationic species. The PES spectra, binding energies, fragmentation energy, electron affinities, vertical and adiabatic detached energies, HOMO-LUMO (H-L) gaps and vibrational spectra are presented and discussed. Our results show that the characteristic planarity for gold clusters is preserved for many of the bimetallic clusters. This study is therefore compared with the case of pure gold for which ample experimental and theoretical data are available. Both experimental and theoretical results obtained here are compared and discussed with previous theoretical studies on the same systems.
RESUMO
We make use of first-principles calculations to study the effects of functionalization and compression on the electronic properties of 2D lattices of Au nanoparticles. We consider Au38 particles capped by methylthiol molecules and possibly functionalized by the dithiolated conjugated molecules benzenedimethanethiol and benzenedicarbothialdehyde. We find that the nonfunctionalized lattices are insulating, with negligible band dispersions even for a compression of 20% of the lattice constant. Distinct behaviors of the dispersion of the lowest conduction band as a function of compression are predicted for functionalized lattices: The band dispersion of the benzenedimethanethiol-functionalized lattice increases considerably with compression, while that of the benzenedicarbothialdehyde-functionalized lattice decreases.