Self-diffusion coefficient of bulk and confined water a critical review of classical molecular simulation studies Tsimpanogiannis, Ioannis N.; Moultos, Othonas A.; Franco, Luís F.M.; Spera, Marcelle B.de M.; Erdös, Mate; Economou, Ioannis G.
We present a new molecular simulation code, Brick-CFCMC, for performing Monte Carlo simulations using state-ofthe-art simulation techniques. The Continuous Fractional Component (CFC) method is implemented for simulations in the NVT/ NPT ensembles, the Gibbs Ensemble, the Grand-Canonical Ensemble, and the Reaction Ensemble. Molecule transfers are facilitated by the use of fractional molecules which significantly improve the efficiency of the simulations. With the CFC method, one can obtain phase equilibria and properties such as chemical potentials and partial molar enthalpies/volumes directly from a single simulation. It is possible to combine trial moves from different ensembles. This enables simulations of phase equilibria in a system where also a chemical reaction takes place. We demonstrate the applicability of our software by investigating the esterification of methanol with acetic acid in a two-phase system.
It is known that thermodynamic properties of a system change upon confinement. To know how, is important for modelling of porous media. We propose to use Hill’s systematic thermodynamic analysis of confined systems to describe two-phase equilibrium in a nanopore. The integral pressure, as defined by the compression energy of a small volume, is then central. We show that the integral pressure is constant along a slit pore with a liquid and vapor in equilibrium, when Young and Young–Laplace’s laws apply. The integral pressure of a bulk fluid in a slit pore at mechanical equilibrium can be understood as the average tangential pressure inside the pore. The pressure at mechanical equilibrium, now named differential pressure, is the average of the trace of the mechanical pressure tensor divided by three as before. Using molecular dynamics simulations, we computed the integral and differential pressures, p ^ and p, respectively, analysing the data with a growing-core methodology. The value of the bulk pressure was confirmed by Gibbs ensemble Monte Carlo simulations. The pressure difference times the volume, V, is the subdivision potential of Hill, ( p − p ^ ) V = ϵ . The combined simulation results confirm that the integral pressure is constant along the pore, and that ϵ / V scales with the inverse pore width. This scaling law will be useful for prediction of thermodynamic properties of confined systems in more complicated geometries.
A computational screening
of 2930 experimentally synthesized metal–organic
frameworks (MOFs) is carried out to find the best-performing structures
for adsorption-driven cooling (AC) applications with methanol and
ethanol as working fluids. The screening methodology consists of four
subsequent screening steps for each adsorbate. At the end of each
step, the most promising MOFs for AC application are selected for
further investigation. In the first step, the structures are selected
on the basis of physical properties (pore limiting diameter). In each
following step, points of the adsorption isotherms of the selected
structures are calculated from Monte Carlo simulations in the grand-canonical
ensemble. The most promising MOFs are selected on the basis of the
working capacity of the structures and the location of the adsorption
step (if present), which can be related to the applicable operational
conditions in AC. Because of the possibility of reversible pore condensation
(first-order phase transition), the mid-density scheme is used to
efficiently and accurately determine the location of the adsorption
step. At the end of the screening procedure, six MOFs with high deliverable
working capacities (∼0.6 mL working fluid in 1 mL structure)
and diverse adsorption step locations are selected for both adsorbates
from the original 2930 structures. Because the highest experimentally
measured deliverable working capacity to date for MOFs with methanol
is ca. 0.45 mL mL–1, the selected six structures
show the potential to improve the efficiency of ACs.
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