An accurate ab initio potential energy surface of HeH2O

We present an accurate calculation of the intermolecular potential surface for the van der Waals complex HeH2O using complete fourth-order Møller-Plesset perturbation theory (MP4) with an efficient basis set containing bond functions. The calculation gives a global minimum at R=3.15 Å, θ=105°, φ=0° (in a Jacobi coordinate system) with a minimum energy De=31.8 cm−1, along with barriers of 13.4 and 12.6 cm−1 for in-plane rotation at θ=0° and 180°, respectively, and a barrier of 20.0 cm−1 for out-of-plane rotation at θ=105°, φ=90°. The potential energy surface is compared with previously published surfaces for HeH2O, and with the potential energy surface for ArH2O.