All calculations are performed using the DMol3 program from
MS (Materials Studio).32,33 The double numerical plus polarization
(DNP) basis set is used in the calculation to describe the
valence orbital of all of the atoms concerned. The numerical
basis sets in DMol3 minimize or even eliminate basis set
superposition error (BSSE), in contrast to Gaussian basis sets,
where BSSE can be a serious problem.34,35 The DFT study with
the DMol3 module is performed with the generalized gradient
corrected approximation (GGA) using the BLYP functional.36,37
The advantage of the BLYP method employed in this study is
that it has a correction term for dispersion forces.38 In this
study, no symmetry constraints are used for any cluster models.
The atom charges are calculated using the approach proposed
by Mulliken.39