DIPOLE, QUADRUPOLE, OCTUPOLE, AND DIPOLE OCTUPOLE POLARIZABILITIES AT REAL AND IMAGINARY FREQUENCIES FOR H, HE, AND H2 AND THE DISPERSION-ENERGY COEFFICIENTS FOR INTERACTIONS BETWEEN THEM

We have calculated certain dynamic polarizabilities (for both real and imaginary frequencies) for H, He, and H-2 and the dispersion-energy coefficients for long-range interactions between them. We have done so in a sum-over-states formalism with explicitly electron-correlated wave functions to describe the states. To be precise, we have determined the dipole (alpha1), quadrupole (alpha2), and octupole (alpha3) Polarizabilities of H and He for real frequencies (omega) in a range between zero and the first electronic-transition frequency and for imaginary frequencies (iomega) on a 32-point Gauss-Legendre grid running from zero to HomegaBAR = 20 E(h), and for H-2, we have found the dipole (alpha), quadrupole (C), and dipole-octupole (E) polarizability tensors for the same real and imaginary frequencies. The dispersion-energy coefficients, obtained by combining the sum-over-states formalism for the polarizabilities with analytic integration over omega, gave values Of C6, C-8, and C-10 for the atom-atom systems; C-6(0), C-6(2), C-8(0), C-8(2) for the atom-diatom systems; and C6, C6', and C6'' for the H-2-H-2 system. Nearly all the results are considered to be more reliable than those hitherto published and some have been obtained for the first time, e.g., C(iomega), E(omega), and E(iomega) for H-2 and C-8(0), C-8(2), and C-8(4) for the H-H-2 system.