In this paper we report the geometries and properties of 40 structural isomers located on the MP2/6-311++G** PES of the carbonic acid dimer. All six possible combinations of carbonic acid monomers were considered. The dimers are divided into six geometrical motifs. Our data suggests that combinations of anti–anti monomers do not necessarily lead to larger stabilization energies in the formation of the dimers. MP2 underestimates the relative binding energies with respect to CCSD(T) by as much as 3.2 kcal mol⁻¹. At least 3 different dimers which may contribute to the stability of carbonic acid are predicted to have significant populations. Binding energy is only directly related to relative stability when comparing dimers formed from the same monomers. Overall stabilization is mainly dictated by attractive electrostatic interactions via cooperative polarization by virtue of the spatial arrangement of the dipole moment components along the polar bonds. Shorter O⋯H bond distances and larger bond orders predicted for the hydrogen bonds directed towards carbonyl groups make for stronger hydrogen bonding than in O⋯H bonds directed towards hydroxyl groups.

A stochastic exploration of the quantum conformational space for the (H₂O)_nLi⁺, n = 3, 4, 5 complexes produced 32 molecular clusters at the B3LYP/6–311++G** and MP2/6–311++G** levels. The first solvation shell is predicted to comprise a maximum of 4 water molecules. Energy decomposition analyses were performed to determine the relationship between the geometrical features of the complexes and the types of interactions responsible for their stabilization. Our findings reveal that electrostatic interactions are major players determining the structures and relative stabilities of the clusters. The formal charge on the Li atom leads to two distinct types of hydrogen bonds, scattered in a wide range of distances (1.61–2.32 Å), in many cases affording H-bonds that are considerably larger and considerably shorter than those in pure water clusters (typically ∼1.97 Å).