On the helium pair potential

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Ab initio calculations of the helium pair potential including extrapolation to the complete basis set (CBS) limit are presented. It is shown that CBS extrapolations of Møller-Plesset calculations using small atomic basis sets supplemented with bond functions give excellent agreement with previously reported empirical and ab initio potentials at very modest computational expense. The CBS extrapolation reduces the basis set superposition correction by an order of magnitude. Our calculated CBS binding energies of 34.66 μ E h (TZDP + bond basis set) and 34.09 μ E h (TZDP + 2d + bond basis set) are very close to the recent empirical estimate of 34.67 μ E h by Aziz, McCourt, and Wong.