Time-Dependent Density Functional Theory Studies of Optical Properties of Ag Nanoparticles: Octahedra, Truncated Octahedra, and Icosahedra

The effect of the size and shape of silver nanoparticles on their optical absorption properties is theoretically investigated to understand the plasmonic properties of these systems. Time-dependent density functional theory (TDDFT) calculations are employed to calculate the optical absorption spectra for a series of silver clusters (Ag-n, n = 6-85) in various charge states whose structures are octahedral, truncated octahedral, and icosahedral. Octahedral Ag-n clusters with n = 6, 19, 44, 85, truncated octahedral Ag-n clusters with n = 13, 38, 55, 79, and icosahedral Ag-n clusters with n = 13, 43, 55 are calculated. Charged systems are considered to obtain closed shell electronic structures. These calculations are performed with the ADF code with the BP86/DZ level of theory in the optimizations and the SAOP functional and LB94 functional in the excitation calculations. A sharp excitation peak originates from a mixture of orbital transitions, and a broad excitation arises from multiple excited states in octahedral, truncated octahedral, and icosahedral Ag-n clusters. We predict that the absorption peak maximum red shifts as the cluster becomes larger and blue shifts as the shape of clusters changed from octahedral to icosahedral.