An ab initio study of He-F-2, Ne-F-2, and Ar-F-2 van der Waals complexes

Single and double excitation coupled-cluster approach with noniterative per turbational treatment of triple excitations [CCSD(T)] has been used to calc ulate the ground state potential energy surfaces for He-F-2, Ne-F-2, and Ar -F-2 van der Waals complexes. Calculations have been performed with the aug mented correlation consistent triple zeta basis sets supplemented with an a dditional set of bond functions (aug-cc-pVTZ+bf), Single point calculations for approximate minima have also been performed with a larger quadruple ze ta basis set (aug-cc-pVQZ+bf), For He-F-2 and Ar-F-2 the CCSD(T) results sh ow that the linear configuration is lower in energy than ther;shaped one. F or Ne-F-2 the CCSD(T) interaction energies of the two configurations are vi rtually the same. The Linear configuration of each complex has been found t o be much more sensitive than the T-shaped one to the changes of the F-F bo nd length with the interaction becoming weaker when the F-F bond length is shortened from its equilibrium value and stronger when it is lengthened. Mo re detailed analysis shows that sensitivity of Component energies such as e xchange, dispersion, and induction is much greater than that of supermolecu le results. High-order correlation corrections have been found to play an i mportant role in determining the relative stability of the linear and T-sha ped configurations. The harmonic approximation zero-point vibrational energ y for He-F-2 exceeds the depth of both wells. For Ne-F-2 the zero-point vib rational energy is greater for the linear configuration and, because of tha t, the complex has a T-shaped ground vibrational state. When the zero-point : vibrational energy is taken into account for the Ar-F-2 complex the linea r and the T-shaped configurations are found to have nearly identical energi es. (C) 1999 American Institute of Physics. [S0021-9606(99)30302-0].