Molecular simulations of confined liquids: An alternative to the grand canonical Monte Carlo simulations

Abstract

Commonly, the confinement effects are studied from the grand canonical Monte Carlo (GCMC) simulations from the computation of the density of liquid in the confined phase. The GCMC modeling and chemical potential (μ) calculations are based on the insertion/deletion of the real and ghost particle, respectively. At high density, i.e., at high pressure or low temperature, the insertions fail from the Widom insertions while the performing methods as expanded method or perturbation approach are not efficient to treat the large and complex molecules. To overcome this problem we use a simple and efficient method to compute the liquid's density in the confined medium. This method does not require the precalculation of μ and is an alternative to the GCMC simulations. From the isothermal-isosurface-isobaric statistical ensemble we consider the explicit framework/liquid external interface to model an explicit liquid's reservoir. In this procedure only the liquid molecules undergo the volume changes while the volume of the framework is kept constant. Therefore, this method is described in the Np(n)AV(f)T statistical ensemble, where N is the number of particles, p(n) is the normal pressure, V(f) is the volume of framework, A is the surface of the solid/fluid interface, and T is the temperature. This approach is applied and validated from the computation of the density of the methanol and water confined in the mesoporous cylindrical silica nanopores and the MIL-53(Cr) metal organic framework type, respectively.

Tunable dielectric constant of water at the nanoscale

“…In both methods ten rates of dehydroxylation were explored from 0% to 100%. Because it has been shown that the polarizability of Na + and water molecules does not impact the structure, dynamics, or dielectric properties of water [23,27], a nonpolarizable model was considered to model Na + [30] while the rigid nonpolarizable TIP4P/2005 model was used to model the water molecules [31,32]. The number of Na + ions corresponded to the number of removed hydrogen atoms of SiOH (236 initially).…”

“…Force field parameters of the silica nanopore are in Refs. [27,28]. Although the silica matrix was subsequently kept rigid, rotation around the Si-O bond of the hydroxyl groups was allowed from the application of a bending potential between Si-O-H. Motion of hydrogen atoms of SiOH was also performed from a stretching potential.…”

“…Chemical potential was calculated from the Widom insertion during the simulation of the water bulk phase in the NpT statistical ensemble at 300 K and 1 bar [27]. This method consists of inserting a ghost particle randomly into a simulation box of N molecules and calculating the interaction energy of this ghost particle with the N molecules.…”

“…This ionic liquid was described by using the AMBER99 force field [39]. Density of IL was computed by means of an anisotropic barostat [27] by contacting the CNT framework with two IL reservoirs at 1 bar.…”

Computational Assessment of Water Desalination Performance of Multi‐Walled Carbon Nanotubes

“…Let us note that the RDFs inside the CNT have higher intensity than in the bulk phase, which results from excluded volume effects. [ 55,72–75 ]…”