Electronic structures and optical properties of Al, Cu, and Ag in zero, two, and three dimensional structures

The electronic structures and associated optical properties of aluminum, copper, and silver were investigated in bulk, thin-film and nanoparticle forms using first-principles band structure methods. The calculations show the progression from continuous bands to subbands to discrete states as spatial confinement is imposed in one and three dimensions. The associated optical properties described by the imaginary component of the dielectric function, epsilon(2)(omega), were also investigated. The interband contributions to epsilon(2)(omega) were calculated from the band structure, while the intraband contributions were calculated using the Drude theory for free electrons. Both contributions to epsilon(2)(omega) are needed to understand the optical properties of metals and to interpret their reflectance spectra. The interband transitions need to be considered to explain reflectivity at energies lower than the plasma frequencies, but not all interband transitions result in reflectance peaks since they are significantly weaker compared to the intraband contributions at lower energies. We have studied the dependence of the density of states on the choice of exchange potentials. In copper, where ultraviolet photoelectron spectroscopy data are available, using a hybrid functional, Heyd-Scuseria-Ernzerhof, leads to better agreement with the experiment than when using the generalized gradient approximation potential, and it reproduces correctly the variation of binding energy of the d electrons going from bulk to thin film. The corresponding dependence exchange potential for silver is less severe. Published by AIP Publishing.