Ab initio molecular dynamics study on Ag (n = 4, 5, 6)

Abstract

Ab initio Molecular Dynamics (MD) method, based on density functional theory (DFT) with planewaves and pseudopotentials, was used to study the stability and internal motion in silver cluster Agn, with n=4-6. Calculations on the neutral, cationic and anionic silver dimer Ag2 show that the bond distance and vibrational frequency calculated by DFT are of good quality. Simulations of Ag4, Ag5, and Ag6 in canonical ensemble reveal distinct characteristics and isomerization paths for each cluster. At a temperature of 800 K, an Ag4 has no definite structure due to internal motion, while for Ag5 and Ag6the clusters maintain the planar structure, with atomic rearrangement observed for Ag5 but not for Ag6. At a temperature of 200 K, Ag4 can exist in two planar structures whilst Ag5 is found to be stable only in the planar form. In contrast Ag6 is stable in both planar trigonal and 3D pentagonal structures. Micro-canonical MD simulation was performed for all three clusters to obtain the vibrational density of states (DOS).