Helium molecules within carbon nanotubes

The ground-state properties of 3He and 4He dimers and trimers in infinite carbon nanotubes are studied. The ground state eigen-functions of a helium atom in tubes of different radii are obtained numerically and then fitted by analytic expressions. Total wave function is assumed to be a product of Jastrow-Feenberg pair correlation and one particle functions. After extensive Monte Carlo (MC) calculation in two successive stages, simple variational MC and diffusion MC it is found that binding depends on the tube radius and it has the maximum for a certain tube width. This radius is between 5 and 7 Angst, and the average distance between atoms in such tubes is ranges from 5 to 10 Angst. The difference in binding between bosons and fermions disappears for R→0