Exact quantum Monte Carlo calculation of the H-He interaction potential

An exact quantum Monte Carlo method is used to calculate the H-He interaction potential under the Born-Oppenheimer approximation. The method used is exact in that it requires no mathematical or physical approximations beyond the Schr\"odinger equation. As in most Monte Carlo methods there is a statistical error which is readily estimated. For the equilibrium internuclear distance of 7.0 bohr the calculated electronic energy is -3.403 7459±{}0.000 0016 hartrees and the corresponding well depth ({ε}/k) is 6.8±{}0.5 K. The calculated potential is consistent with low-energy scattering cross-section measurements [J. P. Toennies, W. Welz, and G. Wolf, Chem. Phys. Lett. 44, 5 (1976)] and with low-temperature diffusion measurements [Hardy et al., Phys. Rev. Lett. 45, 453 (1980)].