Time-dependent coupled Hartree–Fock calculations of multipole polarizabilities and dispersion interactions in van der Waals dimers consisting of He, H2, Ne, and N2

The long-range dispersion interaction coefficients for van der Waals dimers consisting of He, Ne, H2, and N2 have been computed in the time-dependent coupled Hartree–Fock approximation. Static multipole polarizabilities and van der Waals coefficients Cn(n=6,8,10) are presented. The difference between coupled and uncoupled Hartree–Fock results (‘‘apparent’’ correlation) is large in all systems considered and only in the case of Ne the ‘‘true’’ correlation effects are larger. In order to keep the basis set errors in the computed properties smaller than the correlation errors, the basis sets have to be very large. This is demonstrated by using different basis sets for the molecules H2 and N2. The computed van der Waals coefficients for the ten dimers are very accurate, at least the C6 and C8 coefficients, with correlation errors less than 6% for He2, H2–H2, N2–N2, HeH2, HeN2, and H2–N2.