3He, 4He and Mixed Helium Molecules in Two Dimensions

As a continuation of our previous work, the ground state properties of helium molecules consisting of up to 6 helium atoms in two dimensions (2D) are studied. The calculations are performed using variational and diffusion Monte Carlo (MC) procedures successively. For molecules with more than two 3He atoms fixed node diffusion MC (DMC) has been employed. A variety of behavior is observed, depending on the number of 4He and 3He atoms. Bound states are found for all considered molecules. The binding per particle increases continuously with number of particles for 4He, but not for 3He molecules. The particle separation in 4He molecules is about 10 Å, while in 3He molecules it is hundreds of times greater. In mixed molecules, with one or two 3He atoms, 3He prefers to stay further away from the center of mass of the molecule than 4He. In certain cases of mixed molecules, having three and more 3He atoms, energetics and structure indicate a dimerization of 3He.