Abstract: In this paper, we present the results of the prediction of the high-pressure adsorption equilibrium of supercritical gases (Ar, N2, CH4, and CO2) on various activated carbons (BPL, PCB, and Norit R1 extra) at various temperatures using a density-functional-theory-based finite wall thickness (FWT) model. Pore size distribution results of the carbons are taken from our recent previous work,1,2 using this approach for characterization. To validate the model, isotherms calculated from the density functional theory (DFT) approach are comprehensively verified against those determined by grand canonical Monte Carlo (GCMC) simulation, before the theoretical adsorption isotherms of these investigated carbons calculated by the model are compared with the experimental adsorption measurements of the carbons. We illustrate the accuracy and consistency of the FWT model for the prediction of adsorption isotherms of the all investigated gases. The pore network connectivity problem occurring in the examined carbons is also discussed, and on the basis of the success of the predictions assuming a similar pore size distribution for accessible and inaccessible regions, it is suggested that this is largely related to the disordered nature of the carbon.

Abstract: The low-temperature limits of the thermal expansivity, specific heat, and Grüneisen parameter of solid argon, krypton, and xenon are calculated from a quasiharmonic two-body central-force model. The form of our interatomic potential and its predicted thermal and elastic properties are in good agreement with interatomic potentials for argon and krypton derived from solid-state properties plus gas viscosities, second-virial coefficients, and molecular-beam scattering data.

Abstract: A quantum-mechanical variational technique is applied to an Einstein model of a solid, and the heats of sublimation and equations of state of solid Ne, A, Kr, and Xe are calculated at 0°K. Mie-Lennard-Jones 6-12 potentials appropriate to the gas-phase data are used throughout, and the importance of quantum-mechanical effects is discussed; in general, good agreement with experiment is obtained. From the theoretical zero-point energies equivalent Debye temperatures, θ, are calculated, and from the dependence of these θ on volume, Grüneisen constants are computed in good agreement with experiment. Theoretical compressibility curves (at 0°K) are presented, and compared with the available experimental data; in the case of Ne, the only substance for which high-pressure data are available, the agreement is rather good up to 20 k atmos.

Abstract: A potential function is presented that can be used to model both chemical reactions and intermolecular interactions in condensed-phase hydrocarbon systems such as liquids, graphite, and polymers. This potential is derived from a well-known dissociable hydrocarbon force field, the reactive empirical bond-order potential. The extensions include an adaptive treatment of the nonbonded and dihedral-angle interactions, which still allows for covalent bonding interactions. Torsional potentials are introduced via a novel interaction potential that does not require a fixed hybridization state. The resulting model is intended as a first step towards a transferable, empirical potential capable of simulating chemical reactions in a variety of environments. The current implementation has been validated against structural and energetic properties of both gaseous and liquid hydrocarbons, and is expected to prove useful in simulations of hydrocarbon liquids, thin films, and other saturated hydrocarbon systems.

Abstract: A set of combining rules for intermolecular pair potentials recently formulated and shown to be satisfactory for both the Lennard-Jones (12-6) potential and the Morse potential is applied to the exp 6 potential. Examination of the transport properties of the noble gas systems indicates that the same combining rules are also satisfacory for the exp 6 potential and, in fact, superior to the other combining rules previously suggested for the exp 6 potential model.

Abstract: A reanalysis of the transport and equilibrium properties of simple gases was performed in order to obtain more reliable parameter values for two models describing the interatomic potential, the Lennard-Jones (12-6) model and the (exp-6) model. New parameter values for the like interactions were derived from recent accurate viscosity measurements, with an exception for helium. The parameter values for the (exp-6) model differ considerably from the commonly used values given by Mason. The description of the transport properties of neon, argon, krypton and xenon is in general improved with these new parameter values. However, the description of the second virial coefficient of the considered gases with the parameter values from transport properties is rather poor. The parameter values for the unlike interactions could be calculated with several combination rules, confirming the results obtained from recent diffusion measurements in noble-gas mixtures.