Anais do Simpósio Brasileiro de Química Teórica
Anais do XXI Simpósio Brasileiro de Quimica Teórica - Vol. 1 2021

Good afternoon, Rodolfo!

Thank you for the question!

The method of molecular dynamics can capture, in principle, any effect due to changes in the molecular structure of the cation or the anion. However, in this particular work, we used a simplified model, which is called a coarse grained (CG) force field. In a CG model, several atoms are grouped together into a single interaction site. For instance, the [BMIM] cation here is described by only 4 interaction sites, and the anion [BF4] by a single interaction site. This has the advantage to reduce the computational cost of the simulation but has the drawback to loose some atomic details. For instance, there is no explicit hydrogen bond or dipole interactions in this CG model, and the expected effect of hydrogen bonds is taken implicity into dispersion interaction. So, the use of coarse grained models limit the kind of structural change that can be described by the simulation. A small growth of an alkyl chain (going from 4 to 5 C atoms, for instance) will hardly be captured. But a large change, for instance, going from 4 to 8 C atoms in a carbon chain, this can be captured by the model. In this particular force field, is easy to increase the size of alkyl chain by amounts of 4 C atoms at each time. A substitution of an acid hydrogen of imidazolium ring by a CH3 group can be described by using a less attractive parameter for the interaction between imidazolium ring and the anion, but this would need some validation.

For subtle structural changes, I would recommend the use of an atomistic force field, where all atoms are explicit described. We used an atomistic force field on this PCCP work to compare the effect of different anions in the viscosity of ILs: https://pubs.rsc.org/en/content/articlelanding/2021/cp/d1cp01205c

In any case, a classical molecular dynamics simulation will be as good as the force field used. The force field is basically the set of parameters need to describe the inter and intra molecular interactions between different atoms or groups of atoms in the model system. We have now very good force fields to aprotic ILs, but for protic ILs I still see a lot of problems, especially when trying to include effects of electronic polarizability.

I hope I had answered your question, despite I'm not currently working in the problem of gases absorption, there is simulation works related to this. Two authors I personally know and that are working with simulations on this subject are Luciano Tavares (who is also in this conference) and Agílio Pádua. Maybe you can look for their recent works.

Best,

Kalil

Obrigado! Esperamos publicar esses resultados em breve!