CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute
CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute
CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
anions (Cl •− 2 , Br •− 2 & I •− 2 ). 43-44 Quasi Newton Raphson based algorithm has been applied<br />
to carry out geometry optimization for each of these molecular clusters with various<br />
initial thought structures to find out the most stable one. This procedure involves the<br />
calculation of a multi-dimensional potential energy surface for the anionic molecular<br />
cluster and finding a minimum on the surface. The key issue in this search procedure is to<br />
guess a good starting geometry of the cluster, which might converge during the<br />
calculation to a local or the global minimum. In the present calculation, several possible<br />
starting geometries are generated systematically based on different possible threedimensional<br />
structures. In the first case, initial structures are considered where all the<br />
solvent water molecules are at a distance of ionic hydrogen bonding with either of the<br />
two I atoms and far from another solvent molecule to have any inter solvent hydrogen<br />
bonding interaction. In the second case, guess structures are considered where all the<br />
solvent molecules are at a distance of ionic hydrogen bonding with either of the two I<br />
atoms and also at a distance to have an inter water hydrogen bonding interaction. In the<br />
third case, a few solvent water molecules are considered at a distance of ionic hydrogen<br />
bonding with either of the two iodine atoms and far from another solvent water molecule<br />
to have any inter water hydrogen bonding interaction. Rest of the solvent water molecules<br />
are considered at a distance of ionic hydrogen bonding with either of the two I atoms and<br />
also at a distance where inter water hydrogen bonding interaction can exist. No symmetry<br />
restriction has been imposed in the adopted optimization procedure. However, it is to be<br />
noted that the adopted procedure for geometry optimization cannot guarantee to locate<br />
the global minimum energy structure especially for the higher hydrated clusters. Hessian<br />
calculations have been performed for all the optimized minimum energy structures to<br />
21