A complete description of the electric dipole moment (μ), the dipole polarizability (α), the first dipole (β), and the second dipole (γ) hyperpolarizability tensors is reported for the ground state of the water molecule at its equilibrium geometry. Self‐consistent‐field (SCF) and complete fourth‐order many‐body perturbation theory (MP4) values of the independent components are calculated via a finite‐field method from the perturbed energies of the molecule in the presence of a homogeneous electric field. The dependence of the calculated values on the basis set is studied at both the SCF and the MP4 levels. Electron correlation has a strong effect on the hyperpolarizability. Our best SCF values are calculated with a large (13s10p6d2f/9s6p2d)[9s7p6d2f/6s5p2d] basis set comprising 136 contracted Gaussian‐type functions and are 0.7789 e a0 for the dipole moment and 8.531 e2a02 Eh−1, −10.86 e3 a03 Eh−2, and 979 e4 a04 Eh−3 for the mean dipole polarizability and first and second dipole hyperpolarizabilities, respectively. The electron correlation correction to these properties is estimated at −0.055±0.005 e a0, 1.11±0.14 e2 a02 Eh−1, −7.1±1.3 e3 a03 Eh−2, and 749±113 e4 a04 Eh−3. Agreement with experiment is very good for the dipole moment and mean dipole polarizability. As regards the hyperpolarizability, satisfactory agreement with the frequency‐dependent values of Ward and Miller may also be deduced, but further experimental and theoretical work on the dispersion of the hyperpolarizability is needed for an effective rapprochement of theory and experiment.
