RESUMO
The Ewald method has been the cornerstone in molecular simulations for modeling electrostatic interactions of charge-stabilized many-body systems. In the late 1990s, Wolf and collaborators developed an alternative route to describe the long-range nature of electrostatic interactions; from a computational perspective, this method provides a more efficient and straightforward way to implement long-range electrostatic interactions than the Ewald method. Despite these advantages, the validity of the Wolf potential to account for the electrostatic contribution in charged fluids remains controversial. To alleviate this situation, in this contribution, we implement the Wolf summation method to both electrolyte solutions and charged colloids with moderate size and charge asymmetries in order to assess the accuracy and validity of the method. To this end, we verify that the proper selection of parameters within the Wolf method leads to results that are in good agreement with those obtained through the standard Ewald method and the theory of integral equations of simple liquids within the so-called hypernetted chain approximation. Furthermore, we show that the results obtained with the original Wolf method do satisfy the moment conditions described by the Stillinger-Lovett sum rules, which are directly related to the local electroneutrality condition and the electrostatic screening in the Debye-Hückel regime. Hence, the fact that the solution provided by the Wolf method satisfies the first and second moments of Stillinger-Lovett proves, for the first time, the reliability of the method to correctly incorporate the electrostatic contribution in charge-stabilized fluids. This makes the Wolf method a powerful alternative compared to more demanding computational approaches.
RESUMO
The reactive Monte Carlo (RxMC) method was proposed to describe the sorption of gases in solid materials due to the chemical reaction A + B â C. Two models were used to simulate the solid; the first model considered simulations with rigid particles in the solid whereas in the second model the particles were allowed to vibrate inside the solid with a given spring constant, i.e. an Einstein solid was used to simulate the substrate. In both models not only physisorption but also chemisorption of the fluid was observed. Sorption curves, at different spring constants, were simulated and it was noted that sorption was always enhanced with the Einstein solid model. Moreover, an inverse dependent function of the spring constant with the temperature was found. Finally, the second model might be used to explain the unusual sorption behavior observed in actual experimental reactions such as CO2 + Li2O â Li2CO3.