CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute

check the nature of the equilibrium geometry and to generate the IR spectrum. Geometry
of small size hydrated clusters are also calculated incorporating correction due to basis
set superposition error (BSSE) following counterpoise method. 45 Population (P i ) of the
conformers of each size clusters has been calculated based on free energy change (ΔG i ) at
150 K (T) following Boltzmann distribution i. e. P i = Exp(-ΔG i /kT). The weighted
average properties (A w ) is constructed as A w = PiA
. All electronic structure
i
∑
i
calculations have been carried out adopting GAMESS program system on a LINUX
cluster platform. 46
MOLDEN program systems have been used for visualization of
molecular geometry. 47
Triple split Gaussian type basis sets for Br and I atoms are
obtained from the Extensible Computational Chemistry Environment Basis Set Database,
Pacific Northwest Laboratory.
2.3. Results and Discussion
2.3.1.1. Structure of X.nH 2 O (X= Cl •− 2 , Br •− 2 & I •− 2 ) Clusters
To choose a suitable level of theoretical method for these calculations,
geometrical parameters of mono-, di and tri-hydrated clusters of Cl •− 2 , Br •− 2 & I •− 2 are
carried out following 30 correlated density functionals (hybrid, pure and meta generalized
gradient approximation density functionals). The calculated geometrical parameters are
compared to that of at second-order Moller–Plesset perturbation (MP2) theory adopting
6-311++G(d,p) basis functions (I atom treated by 6-311 basis set). It is observed that
Becke’s half-and-half (BHH) non-local exchange and Lee–Yang–Parr (LYP) non-local
correlation functionals (BHHLYP) perform well to describe these clusters producing
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