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

We report an extensive investigation of the electric dipole moment (mu(alph a)), static polarizability (alpha(alpha beta)), and hyperpolarizability (be ta(alpha beta gamma) and gamma(alpha beta gamma delta)) 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] bas is 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 mu=1.0706ea(0), mean and anisotropy of the dipole polarizability <(alpha)over bar> = 16.98 and Delta alpha=2.69e(2)a( 0)(2)E(h)(-1), first hyperpolarizability (in the direction of the dipole mo ment vector) <(beta)over bar>=-2.9e(3)a(0)(3)E(h)(-2), and mean second dipo le hyperpolarizability <(gamma)over bar>=1906e(4)a(0)(4)E(h)(-3). Very larg e electron correlation effects are observed for the hyperpolarizability. At the CCSD(T) level, coupled-cluster theory with single, double and perturba tively linked triple excitations, our best values are mu=1.0204ea(0), <(alp ha)over bar>=19.54, and Delta alpha=3.06e(2)a(0)(2)E(h)(-1), <(beta)over ba r>=-6.5e(3)a(0)(3)E(h)(-2), and <(gamma)over bar>=3669e(4)a(0)(4)E(h)(-3). <(alpha)over bar>((H2O)(2)) and <(gamma)over bar>((H2O)(2)) are not drastic ally different than twice the size of <(alpha)over bar>(H2O) and <(gamma)ov er bar>(H2O). Our efforts to estimate the interaction properties of two wat er molecules in the dimer lead to the conclusion that <(alpha)over bar>(int er) and <(gamma)over bar>(inter) are rather small. Further calculations at a relaxed monomer geometry (REMG) corroborate this conclusion. We have full y 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. (C) 2000 American Institute of Physics. [S0021-9606(00)30429-9].