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The phase diagram of the first layer of 4He adsorbed on a single graphene sheet has been calculated by a series of diffusion Monte Carlo calculations including corrugation effects. Since the number of C-He interactions is smaller than in graphite, the binding energy of 4He atoms to graphene is reduced approximately 13.4 K per helium atom. Our results indicate that the phase diagram is qualitatively similar to that of helium on top of graphite. A two-dimensional liquid film on graphene is predicted to be metastable with respect to the commensurate solid but the difference in energy between both phases is very small, opening the possibility of such a liquid film to be experimentally observed.

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We carried out molecular dynamics simulations to describe the properties of water inside a narrow graphite channel. Two stable phases were found: a low-density one made of water clusters adsorbed on the graphite sheets and a liquid one that fills the entire channel, forming several layers around a bulk-like region. We analyzed the interfacial structure, orientational order, water residence times in several regions, and hydrogen bonding of this last water phase, calculating also a quantity of electrochemical interest, the probability of electron tunneling through interfacial water. The results are in good qualitative agreement with the available experimental data.

Electric and dielectric properties and microscopic dynamics of liquid water confined between graphite slabs are analyzed by means of molecular dynamics simulations for several graphite-graphite separations at ambient conditions. The electric potential across the interface shows oscillations due to water layering, and the overall potential drop is about -0.28 V. The total dielectric constant is larger than the corresponding value for the bulklike internal region of the system. This is mainly due to the preferential orientations of water nearest the graphite walls. Estimation of the capacitance of the system is reported, indicating large variations for the different adsorption layers. The main trend observed concerning water diffusion is 2-fold: on one hand, the overall diffusion of water is markedly smaller for the closest graphite-graphite separations, and on the other hand, water molecules diffuse in interfaces slightly slower than those in the bulklike internal areas. Molecular reorientational times are generally larger than those corresponding to those of unconstrained bulk water. The analysis of spectral densities revealed significant spectral shifts, compared to the bands in unconstrained water, in different frequency regions, and associated to confinement effects. These findings are important because of the scarce information available from experimental, theoretical, and computer simulation research into the dielectric and dynamical properties of confined water.

Using quantum Monte Carlo we have studied the superfluid density of the first layer of 4 He and H2 adsorbed on graphene and graphite. Our main focus has been on the equilibrium ground state of the system, which corresponds to a registered √ 3 × √ 3 phase. The perfect solid phase of H2 shows no superfluid signal whereas 4 He has a finite but small superfluid fraction (0.67%). The introduction of vacancies in the crystal makes the superfluidity increase, showing values as large as 14 % in 4 He without destroying the spatial solid order.

We report the results of a calculation of the vibrational and rotational spectra of water confined in carbon nanotubes. Water has been modeled with a flexible version of the simple point charge model of Berendsen et al., while the carbon nanotubes are taken to be soft potential walls interacting with water through a Lennard-Jones-type potential. The comparison of the computed absorption line shapes with the corresponding ones of liquid bulk water shows significant shifts in the positions of the spectral bands directly related to the tube radii.