Electrostatic guidelines and molecular tailoring for density functional investigation of structures and energetics of (Li)_n clusters

Abstract

A molecular electrostatic potential (MESP)-guided method for building metal aggregates is proposed and tested on prototype lithium (Li)_n clusters from n = 4 to 58. The smaller clusters are subsequently subjected to direct density functional theory based geometry optimization, while the larger ones are optimized via molecular tailoring approach (MTA). The calculations are performed using PW91-PW91 as well as B3LYP functionals, and the trends in the interaction energies are found to be similar. The MESP-guided model for building metal clusters is validated by comparing the resulting cluster geometries with the ones reported in the literature up to n = 20. A comparison of the ionization potential and polarizability (up to n = 22) with their experimental counterparts shows a fairly good agreement. A new MTA-based scheme for calculating the ionization potential and polarizability values of large metal clusters is proposed and tested on Li₄₀ and Li₅₈ clusters. Further, the existence of "magic numbered clusters" up to n = 22 is justified in terms of "maximum hardness principle" as well based on molecular electron density topography and distance descriptors.