Ab initio Study of the Li-CO van der Waals Complex

The adiabatic potential energy surface (PES) of the Li-CO complex in the van der Waals region, described by Jacobi coordinates (r = 1.15 Å, R, Θ), was investigated using the supermolecular coupled-clusters CCSD(T) method. Our calculations indicate minima for bent arrangements. The first minimum was found on the carbon side of CO molecule at R = 5.27 Å (Θ = 50.7°) with a well depth of De = -167.2 μEh. The second minimum is indicated at R = 5.35 Å (Θ = 148.7°) with a well depth of De = -121.9 μEh. The saddle point is localised at θ = 111.5° and R = 5.35 Å. The physical origin of the weak interaction studied was analysed by the intermolecular perturbation theory based on the single determinant UHF wave function. The separation of the interaction energies shows that the locations of the predicted stable bent structures are primarily determined by the anisotropy of the repulsive Heitler-London exchange penetration and attractive dispersion and induction energy components.