Accurate relativistic many-body calculations of van der Waals coefficients C₈ and C₁0 for alkali-metal dimers

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We consider long-range interactions between two alkali-metal atoms in their respective ground states. We extend the previous relativistic many-body calculations of C₆ dispersion coefficients [Phys.Rev. Lett. 82, 3589 (1999)] to higher-multipole coefficients C₈ and C₁0. A special attention is paid to usually omitted contribution of core-excited states. We calculate this contribution within relativistic random-phase approximation and demonstrate that for heavy atoms core excitations contribute as much as 10% to the dispersion coefficients. We tabulate results for both homonuclear and heteronuclear dimers and estimate theoretical uncertainties. The estimated uncertainties for C₈ coefficients range from 0.5% for Li₂ to 4% for Cs₂.