Eh. Teunissen et Apj. Jansen, LARGE BASIS-SETS AND GEOMETRY OPTIMIZATIONS IN EMBEDDED-CLUSTER CALCULATIONS, International journal of quantum chemistry, 54(1), 1995, pp. 73-81
In the embedded cluster method, a cluster is embedded in a correction
potential. This potential adds the long-range electrostatic forces of
the crystal and subtracts the electrostatic potential of the boundary
errors of the cluster. The correction potential is calculated from the
wave function of the cluster and the crystal. So far, the method has
only been used on a cluster having the same geometry and basis set as
that of the crystal. Here, we calculated the adsorption energies of NH
3 and NH4+ on an embedded zeolite cluster with different basis sets an
d modified geometries. We showed that a mixed basis set, a basis set h
aving a large basis set on the atoms around the adsorption site and a
minimal basis set on the atoms of the boundary of the cluster, yields
adsorption energies close to that of the large basis set. The optimize
d geometries of the zeolite acidic site were almost equal for the none
mbedded cluster, the embedded cluster, and the crystal. By combining t
he mixed basis set with a partial geometry optimization, an improved d
escription of the adsorption process is obtained. (C) 1995 John Wiley
& Sons, Inc.