Determination of potential-energy surface of molecules in an applied field on the basis of virial relations

The quantum-mechanical virial theorem (in diagonal and nondiagonal forms) for molecules in an external, weak, uniform electric field is used for obtaining the analytical expression of the potentialenergy surface in the Hartree–Fock–Roothaan one-determinantal approximation. The polarizability tensor components of the H₂O molecule are computed on this basis. The dependence of basing the atomic orbitals upon the intensity of the applied field lead to good coincidence of results with the data of near Hartree–Fock calculations.