CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute

structure with lower in energy has been accepted while structures with higher energies
have been accepted at a probability determined by the Boltzmann factor. Random
structures have been generated by carrying out Monte Carlo steps at a high temperature
(2,000 K) for more than 8000 steps. Both configuration interaction with single electron
excitation (CIS) method and time dependent density functional theory (TDDFT) has been
adopted for predicting a few low lying excited states of all the clusters, reported in this
chapter.
5.3. Results and Discussion
5.3.1. Structure
Various possible initial structures of Cl •− 2 .nH 2 O clusters (n=1-11) are considered
for global geometry optimization and a number of minimum energy structures
(conformers) are obtained. The global minimum energy structure of each size of hydrated
cluster, Cl •− 2 .nH 2 O (n=1-11) at BHHLYP/6-311++G(d,p) is displayed in Fig. 5.1.
Structures of Cl •− 2 .nH 2 O clusters (n=1-5) are also very close to the reported structures by
Johnson and co-workers. 24 It is observed that the Cl •− 2 .nH 2 O clusters are stabilized by
double hydrogen bonding (DHB), single hydrogen bonding (SHB) and inter water
hydrogen bonding (WHB). Conformation having H-bonded water network (WHB
arrangements) are more stable over the other structures where H 2 O units are connected to
the anion moiety independently either by SHB or DHB for a particular size of cluster. H-
bonded water network having two, three or four H 2 O units are present in the different
conformers of these clusters. Hydrated cluster having cyclic water network units is the
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