Journal of Physical Chemistry A, Vol.119, No.29, 8163-8173, 2015
Time-Dependent Density Functional Theory Investigation of the Electronic Structure and Chiroptical Properties of Curved and Helical Silver Nanowires
Time-dependent density functional theory methods are employed to examine the evolution of the absorption and circular dichroism (CD) spectra of neutral bare silver helical nanostructures as a function of their geometrical parameters. Calculations of excited states to determine optical absorption and CD spectra were performed using the SAOP/TZP level of theory. In our model, the geometry of the helical silver chain is dependent on the Ag-Ag-Ag bond angle and the Ag-Ag-Ag-Ag dihedral angle. The influence of different geometrical structures on the optical absorption and CD spectra were studied for helical and planar Ag-8. Silver nanowires Ag-n (n = 4, 6, 8, 10, 12) were examined to determine the effect of the helical chain length on the electronic properties. The results show that when the metal atomic chain loses planarity, strong CD signals arise; the intensities of the CD peaks for these structures are strongly affected by the shape and length of the silver nanowires. The theoretically predicted CD spectra of the nonplanar Ag-4 and Ag-6 model systems show good agreement in spectral shapes and reasonable agreement in peak locations compared to experimental data for silver-DNA clusters. However, the theoretical and experimental results for the longer Ag-12 wire show larger differences in the peak locations, which could potentially be caused by effects such as the presence of DNA and cationic silver atoms in the experimental system.