An ab-initio study of photoabsorption spectrum of ultra small CdS clusters

An ab-initio calculation of photoabsorption, and absorption threshold has been performed for (CdS)n, n=1–8, atomic clusters using time-dependent density functional formalism. We used both time-propagation method as well as the Casida's linear theory formalism to compute photoabsorption spectrum for energies up to 15 eV. The photoabsorption exhibits prominent peaks for energies between 0 and 15 eV, and validity too of our methodology is not under any kind of question mark, in this energy range. The computed results from both time-propagation method as well as the Casida's formalism are found in good agreement with each other as well as with recently reported photoabsorption experimental data on (CdS)n, atomic clusters, for UV frequency range. Our results show that the absorption thresholds lie in between 2.08 and 6.29 eV, and first ionization energies of clusters varies from 3.14 to 8.92 eV for all (CdS)n clusters.