Monte Carlo simulation of a helium film on graphite

Quasi-one-dimensional4Heinside carbon nanotubes

“…Our results indicate that for large enough densities 6 (λ > 0.358Å −1 ) both the 1D and the tube arrangements have a localized (solid) phase and that the discontinuity in the density (if any) is surely very small. This is in agreement with the results discussed by Withlock et al [21] about the reduction of the size of this discontinuity from three to two dimensions: in 3D is fairly large, being considerably smaller in a purely 2D system. In 1D, we observe a further reduction towards a continuous or a quasi-continuous transition.…”

“…with Ψ c (R) = N i exp(−c r 2 i ) (r i being the radial distance of the particle to the center), that The binding energy of a single 4 He atom in graphite is E G B = 140.74 K [21], whereas in the nanotube we are studying is roughly three times larger, E T B = 429.97 K, a significant 4 difference that has been dramatically observed in the desorption experiment of Teizel et al [12]. On the other hand, the departure of the real 3D systems ( 4 He in graphite or a nanotube) from the idealized 2D or 1D liquids can be quantified by means of the parameter…”

Phase Diagrams of 4He on Flat and Curved Environments

“…In fact, as it can be seen in Table 1, both energies are within each other error bars. However, for tubes whose radius is lower than the corresponding to a (10, 10) one, the lowest energy per particle correspond to an incommensurate solid (the (8,8) case is displayed as an example). On the other hand, the opposite happens for wider radii, of which the (12, 12) is chosen as a representative.…”

“…In the first studies of adsorption on graphite [8,12], a smoothed interaction that approached the C-He pair interaction sum was used. However, more recent studies [1,11,18] substitute this integrated potential by explicit pair sums that, in practice, can be tabulated in a grid for an efficient use in the simulation.…”

“…The main uncertainties in these microscopic approaches derive from the possible deficiencies in the adsorbate atom-surface interaction. In the first studies [8][9][10]12] it was usual to work with a smoothed interaction that depends only on the distance of the atom to the carbon plane. However, this potential is not able to generate a satisfactory phase diagram because no corrugation is present.…”