Static hyperpolarizability of the water dimer and the interaction hyperpolarizability of two water molecules

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Abstract
We report an extensive investigation of the electric dipole moment (μα), static polarizability (ααβ), and hyperpolarizability (βαβγ and γαβγδ) of the water dimer. Calculations were performed at both rigid and relaxed monomer geometries. At the rigid monomer geometry (RIMG), a very large [9s6p6d4f/6s5p3d2 f] basis set consisting of 370 Gaussian-type functions is thought to provide self-consistent field (SCF) values very close to the Hartree–Fock limit for all properties: total dipole moment μ=1.0706ea0, mean and anisotropy of the dipole polarizability ᾱ=16.98 and Δα=2.69e2a02Eh−1, first hyperpolarizability (in the direction of the dipole moment vector) β̄=−2.9e3a03Eh−2, and mean second dipole hyperpolarizability γ̄=1906e4a04Eh−3. Very large electron correlation effects are observed for the hyperpolarizability. At the CCSD(T) level, coupled-cluster theory with single, double and perturbatively linked triple excitations, our best values are μ=1.0204ea0, ᾱ=19.54, and Δα=3.06e2a02Eh−1, β̄=−6.5e3a03Eh−2, and γ̄=3669e4a04Eh−3. ᾱ((H2O)2) and γ̄((H2O)2) are not drastically different than twice the size of ᾱ(H2O) and γ̄(H2O). Our efforts to estimate the interaction properties of two water molecules in the dimer lead to the conclusion that ᾱinter and γ̄inter are rather small. Further calculations at a relaxed monomer geometry (REMG) corroborate this conclusion. We have fully explored basis set effects at all levels of theory and for all properties. We rely on a sequence of small-sized but sufficiently flexible basis sets in order to propose reliable computational strategies for the extension of electric property calculations to large water clusters.