We have analyzed the modifications of interaction energy between a molecule of hydrogen and graphene layers partially substituted by boron. We show that the presence of boron modifies the symmetry of the energy landscape. It is due to both the larger boron size (with respect to carbon) and its stronger interaction with hydrogen molecules. The changes of energy surface are not confined to the neighborhood of substituted sites but extend over several graphene carbon sites, making the surface more heterogeneous. We show that the average increase of adsorption energy could meet DOE targets for hydrogen storage if a partial charge transfer between boron and hydrogen occurs during adsorption.

We discuss molecular dynamics (MD) computer simulations of a tetracosane (C24H50) monolayer physisorbed onto the basal plane of graphite. The adlayer molecules are simulated with explicit hydrogens, and the graphite substrate is represented as an all-atom structure having six graphene layers. The tetracosane dynamics modeled in the fully atomistic manner agree well with experiment. The low-temperature ordered solid organizes into a rectangularly centered structure that is not commensurate with underlying graphite. Above T= 200 K, as the molecules start to lose their translational and orientational order via gauche defect formation a weak smectic mesophase (observed experimentally but never reproduced in united atom (UA) simulations) appears. The phase behavior of the adsorbed layer is critically sensitive to the way the electrostatic interactions are included in the model. If the electrostatic charges are set to zero (as for a UA force field), then the melting temperature increases by similar to 70 K with respect to the experimental value. When the nonbonded 1-4 interaction is not scaled, the melting temperature decreases by similar to 90 K. If the scaling factor is set to 0.5, then melting occurs at T = 350 K, in very food agreement with experimental data.

Molecular Dynamics (MD) simulations of tetracosane (C24H50) monolayer physisorbed on graphite are carried out. C24H50 molecules are simulated with explicit hydrogens and the graphite is represented by six graphene layers. We focus our analysis on the microscopic mechanism of melting, experimentally observed at T = 340 K. We are looking for the pre-melting transformations and analyze if there is a correlation between translational disordering of molecules and their internal degrees of freedom. We analyze several order parameters and their fluctuations along the MD trajectories. We show that the all atom representation of C24H50 is much more sensitive to the model of intramolecular interactions than united atom model. In particular two components: electrostatic forces and scaled 1-4 internal non-bonded interactions can shift melting temperature by several tenths of degree. A correlation between molecular stiffness and the intermolecular forces causes molecules’ footprint reduction during melting which involves a simultaneous lost of intramolecular and translational order. This cooperative mechanism is related to an abrupt increase of gauche defects within the central region of the chain.

We present results of grand canonical Monte Carlo simulations of rare gases (He, Ne, Ar, Kr and Xe) adsorption in carbon nanotubes. The interaction model includes both quantum effects (via effective Feymann-Hibbs potential) and the atomic roughness of the tube. We show that the quantum contribution to interactions does not suppress the energetic corrugation of carbon nanotube but decreases only its average strength. In the case of Ne, the phase diagram and, in particular, the melting temperature for layers adsorbed on and within an individual tube does not depend on tube chirality. However, the structure of layers adsorbed on outer surface of the tube is strongly related to the atomic structure of the underlying tube.

We present results of grand canonical Monte Carlo simulations of adsorption in cylindrical pores with rough surface modeled by a parametric lattice-site approach. The sites are randomly distributed over the pore walls. They could be attractive, neutral or repulsive with respect to the smooth pore model. Each site is characterized by two amplitudes (structural and energetic) which modify locally the structure and energetic properties of the surface. The results presented here show how different parameters of the model affect the mechanism of adsorption and, consequently, the form of the isotherm.