The three-dimensional ground state potential energy surfaces for He-Cl-2, N
e-Cl-2, and Ar-Cl-2 have been calculated using the single and double excita
tion coupled-cluster approach with noniterative perturbational treatment of
triple excitations [CCSD(T)]. Calculations have been performed with the au
gmented correlation consistent triple zeta basis sets supplemented with an
additional set of bond functions. Single point calculations for approximate
minima have also been performed with several other basis sets including th
e quadruple zeta basis set (aug-cc-pVQZ) with bond functions. For He-Cl-2 a
nd Ar-Cl-2 the CCSD(T) results show that the linear configuration is lower
in energy than the T-shaped one. For Ne-Cl-2 the CCSD(T) approach predicts
the T-shaped configuration to be lower in energy. The linear configuration
has been found to be more sensitive than the T-shaped one to the changes of
the Cl-Cl bond length with the interaction becoming weaker when the Cl-Cl
bond length is shortened from its equilibrium value and stronger when it is
lengthened. More detailed analysis shows that sensitivity of component ene
rgies such as exchange, dispersion, and induction is much greater than that
of supermolecule results. The interaction in the T-shaped configuration be
comes slightly stronger for shorter Cl-Cl bonds. For He-Cl-2 and Ar-Cl-2 th
e larger zero-point vibrational energy of the linear configuration is respo
nsible for making the T-shaped configuration the ground vibrational state.
Vibrational effects further increase the difference in energy between the g
round state T-shaped configuration of Ne-Cl-2 and its linear counterpart. (
C) 1999 American Institute of Physics. [S0021-9606(99)30216-6].