CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute

In all the clusters, K.nNH 3 (n=1-6) the K-N distance varies from 2.8–3.0 Å. The
energy of K..NH 3 interaction is calculated to vary from 5-6 kcal/mol and the energy due
to hydrogen bonding between two NH 3 molecules is ~1 kcal/mol. Thus, the ammoniated
cluster is dominantly stabilized by the solute-solvent interaction rather than solventsolvent
interaction. The solvent-solvent interaction energy plays significant role in the
larger size clusters though.
6.3.2. Solvent Stabilization Energy
The solvent stabilization energy of K.nNH 3 clusters can be expressed as
solv
E = EK. nNH
− ( nENH + EK
),
3 3
where E
K.
nNH
, E
3 NH3 and E K
refer to the total energy of the optimized cluster, K.nNH 3 ,
the energy of a single NH 3 molecule at equilibrium geometrical and the energy of K
atom, respectively. Thus, calculated E solv essentially refers to the total interaction energy
of the solute with n solvent NH 3 units around it in the ammoniated cluster of size n. The
calculated weighted average solvent stabilization energy ( E solv w
) of the K.nNH 3 (n=1-6)
clusters are supplied in Table 6.1. The plot for the variation of E solv w
vs. n is shown in Fig.
6.2-A. The weight factor of a minimum energy structure within a particular size (n) of
cluster is calculated based on the statistical population of the conformer at 150 K. The
best-fitted linear plot having correlation coefficient greater than 0.99 is
E solv w
= 2.06 + 5.35 n,
where E solv w
is expressed in kcal/mol and n is the cluster size.
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