Theoretical study of Au4 thymine, Au20 and Ag20 uracil and thymine complexes for surface enhanced Raman scattering

A Density Functional Theory (DFT) study using the relativistic effective core potentials (RECPs) is performed with an aim to understand the relative energies and gain deeper insight of the preferential binding of the sites of nucleobases towards particular sites of tetrahedral twenty atom Au and Ag clusters and Au-4 cluster using reactivity descriptors. Such calculations carry high values towards understanding the relativistic effects of the Au atom towards the Surface Enhanced Raman spectrum (SERS) of small molecules like uracil and thymine when they are bound to the heavy metal clusters, viz., Au and Ag. The relative stabilities based on the prediction of the reactivity descriptors are analyzed. For Au-4, scattering activities exhibit further enhancement in absence of relativistic mass-velocity contractions and Darwin corrections as implemented in LANL2DZ ECPS for Au in complexes, indicating the importance of relativistic effects in Au for proper evaluation of SERS and explains Ag acting as a better surface than Au for SERS. (C) 2017 Published by Elsevier B.V.