A new force field for the adsorption of H2, O2, N2, CO, H2O, and H2S gases on alkali doped carbon nanotubes

The main goal of this work is the generation of a new force field data set to the interaction of several gases such as H-2, O-2, N-2, CO, H2O, and H2S with alkali cation-doped carbon nanotubes (CNTs) using ab initio calculations at the MP2(full)/6-311++G(d,p) level of theory. Different alkali cations including Li+, Na+, K+ and Cs+ were used to dope in the CNT. The calculated potential energy curve for the interaction of each gas molecule with each alkali cation-doped CNTs was fitted to an analytical potential function to obtain the parameters of the potential function. A modified Morse potential function was selected for the fitting in which the electrostatic interactions has been accounted by adding the beta/r term to the Morse potential. The accuracy of the calculated force field was checked via Grand Canonical-Monte Carlo (GCMC) simulation of the H-2 adsorption on Li-doped graphite and Li-doped CNT. The results of these simulations were compared with the experimental measurements and the closeness of the simulation results with the experimental data indicated the accuracy of the proposed force field. The main merit of this work is the derivation of a specific force field for interaction of each of six gases with four alkali cation-doped CNT, which can be used in molecular simulation of these 24 of systems. The simulation results showed the increase of the H-2 adsorption capacity of nanotube and graphite up to 50% and 10%, respectively, due to the insertion of Li ions. [GRAPHICS] .