Assessment of the accuracy of long-range corrected functionals for describing the electronic and optical properties of silver clusters

The absorption spectra and ionization potentials of silver clusters Ag n ( n = 4 - 20 ) are examined in the framework of density-functional theory (DFT) using several different methods of representing the exchange-correlation functional. Three different types of exchange-correlation functionals are used: those including gradient corrections to the density in the generalized gradient approximation, global hybrid functionals mixing in a portion of the Hartree-Fock exchange, and long-range-corrected (LC-) functionals. Comparison of ionization potentials calculated using DFT with those derived from experiments demonstrates that LC-functionals more accurately represent the electronic structure of the silver clusters studied. Absorption spectra are compared with both experimental spectra and those derived using higher level theoretical calculations showing that the LC-functionals appear to correctly describe the optical transitions in the gas phase, particularly when a small redshift in the experimental spectrum is accounted for due to matrix effects. It is also demonstrated that the LC-hybrid functionals significantly reduce the occurrence of spurious states in the optical absorbance spectrum while maintaining the intensity of plasmon like features of the spectra for larger silver clusters.