A density-functional approach and canonical Monte Carlo simulations are presented for describing the ionic microscopic structure around the DNA molecule immersed in mixed-size counterion solutions. In the density-functional approach, the hard-sphere contribution to the Helmholtz energy functional is obtained from the modified fundamental measure theory [Y.-X. Yu and J. Z. Wu, J. Chem. Phys. 117, 10156 (2002)], and the electrostatic contribution is evaluated through a quadratic functional Taylor expansion. The new theory is suitable to the systems containing ions of arbitrary sizes and valences. In the established canonical Monte Carlo simulation, an iterative self-consistent method is used to evaluate the long-range energy, and another iterative algorithm is adopted to obtain desired bulk ionic concentrations. The ion distributions from the density-functional theory (DFT) are in good agreement with those from the corresponding Monte Carlo (MC) simulations. It is found that the ratio of the bulk concentrations of two species of counterions (cations) makes significant contribution to the ion distributions in the vicinity of DNA. Comparisons with the electrostatic potential profiles from the MC simulations show that the accuracy of the DFT becomes low when a small divalent cation exists. Both the DFT and MC simulation results illustrate that the electrostatic potential at the surface of DNA increases as the anion diameter or the total cation concentration is increased and decreases as the diameter of one cation species is increased. The calculation of electrostatic potential using real ion diameters shows that the accuracy of DFT predictions for divalent ions is also acceptable.

The equilibrium selective adsorption and fluxes of oxygen/nitrogen binary gas mixtures through carbon membranes are investigated at 303 K, respectively, using a grand canonical Monte Carlo simulation and a dual control volume grand canonical molecular dynamics method. The carbon membrane pores are modeled as slit-like pores with a two-dimensional structure where carbon atoms are placed according to the structure of graphite layers. The effect of the membrane thickness, bulk pressure, and pore width on the equilibrium selective adsorption and dynamic separation factor is discussed. Meanwhile a new iteration approach to calculate the flux and dynamic separation factor of binary gas mixtures through membranes is proposed, by which we can simulate the permeation and fluxes of gases through the membranes in the presence of pressure gradient and consider the effect of pressure and composition of low-pressure side in the meantime. The simulated results show that bulk pressure and membrane thickness have no effect on the equilibrium selectivity, but they have a great effect on the fluxes and dynamic separation factors of gases. The pore width impacts the equilibrium selectivity and dynamic separation factors strongly, especially when the pore width is very small. Molecular sieving dominates the separation of oxygen/nitrogen in non-equilibrium simulations. But due to the comparable molecular size of oxygen and nitrogen, we have to modify the carbon membranes in order to improve dynamic separation of atmosphere.

The structural properties and transport properties of electrolyte solutions are investigated by smart Brownian dynamics simulation based on the primitive model. To test the simulation program, the radial distribution functions of ions g+−(r) and g++(r) for KCl solution are calculated and compared with the results of previous simulations. And then, the effects of ions diameter and concentration on the structural properties and transport properties of electrolyte solution at 298K are extensively simulated. The results indicate that both the radial distribution function and the self-diffusion coefficient are more sensitive to the ion size than salt concentration. As the radius ratio of cation to anion increases, self-diffusion coefficients of both cation and anion become larger.

In this paper, the separation of binary gas mixture carbon monoxide and hydrogen using single-walled carbon nanotubes (SWNTs) is studied by grand canonical Monte Carlo (GCMC) simulation. All of the particle–particle interactions between hydrogen, carbon monoxide and carbon are modeled with Lennard–Jones potential. Widom test particle method in NVT ensemble is used in determining chemical potentials of the two components of the fluid. It can be concluded from the adsorption isotherms at 293.15Kthat the selectivity of carbon monoxide decreases with the increase of the bulk pressure. In the adsorption isostatics at 0.157MPa, the selectivity has a maximum along with the increase of temperature. However, to given pressure and temperature, the selectivity fluctuates violently with different van der Waals (VDW) distances or diameters of carbon nanotubes. For example, at 0.157MPa, 293.15 K, diameter of 0.892 nm and VDW distance of 1 nm, with the feed containing hydrogen and carbon monoxide both 50 mol%, carbon monoxide could be enriched up to 98 mol% in the adsorbate, so that the selectivity comes to 60. It can be indicated that carbon nanotube, as a novel material developed in the past 10 years, can make a very effective separation tool of certain gas mixtures.

The solubilities of oxygen in 0.2, 0.5, 0.7 and 1.0MNa2CO3 solution have been measured at 300.15K and under pressures up to 10MPa using a magnetically stirred autoclave and a direct sampling technique. The accuracy of apparatuswas verified by duplicating the solubility of oxygen in purewater in literature. The experimental data of the solubility of oxygen in aqueous sodium carbonate solution were shown that the solubility of oxygen increases with increasing pressure and decreases with increasing salt concentration due to salting-out effect. The experimentally measured data were satisfactorily compared with the predicted values by our model based on non-primitive mean spherical approximation (MSA) and perturbation theory.