Official websites use .gov
A .gov website belongs to an official government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.
TMMC: Reference Adsorption Isotherms for N2/CO2 Mixtures in Metal-organic Frameworks
Transition-Matrix Monte Carlo (TMMC) simulations of binary mixtures of N2 and CO2 [1-10] were performed at T = 300 K and 350 K in the ZIF-8 metal-organic framework (MOF). The main result of a GC-TMMC simulation is the particle number probability distribution (PNPD), which is constructed by stitching together the particle number distributions from each window. The adsorption isotherm may be determined from the PNPD [10].
Simulations used different combinations of Monte Carlo moves depending on the number of particles, as described below. Low density windows used a conventional set of moves (i.e., no configurational bias) whereas high density windows used a configurational bias strategy known as Dual-cut configurational bias (DCCB) Monte Carlo [13]. Additionally, low-density windows started in Wang-Landau biasing mode to quickly generate a guess of the PNPD, later switching to TMMC mode; data from the TMMC phase of the simulation was saved and reported here.
Other key simulation details common to all simulations are given below:
| Fluid Model | TraPPE N2 and CO2[11] | |
| Lennard-Jones cutoff | 12A (cut potential, no tail correction) | |
| Ewald Parameters | Set according to DL_POLY recipe [15], with relative tolerance 10-5 | |
| Trial Move Types | ALL: Translation, Pivot rotation Grand-Canonical: N < Nmax/2: Standard Insertion and Deletion N > Nmax/2: Dual-cut Configurational Bias (DCCB) [13] Growth Isochoric Semigrand Canonical: Identity-change | |
| DCCB Details | Number of trials per atom: 4 Reference Potential: Lennard-Jones + Ewald Realspace Cutoff Radius for Reference Potential: 4.5A | |
| Bias update freq | 1.0e5 | |
| Simulation Length | 200 sweeps [FEASST] | |
| Physical Parameters | CODATA 2018 [12] | |
Simulations were performed using the open-source FEASST Monte Carlo engine [11], using version 0.21.1 or 0.24.1.
The adsorbent MOF was reconstructed from publicly-available crystal structures and replicated to ensure that the simulation cell was at least twice the cutoff radius in all dimensions. Forcefields for each MOF were taken from published literature. The MOF structure and forcefield are provided in FEASST particle files in the data repository associated with this page (see "Data Availability" below). Coulombic interactions were handled using the Ewald summation method [2,3] (parameters listed in the metadata files). Lorentz-Berthelot combining rules were used to set the unlike-atom Lennard-Jones parameters.
Simulation details specific to each MOF
| ZIF-8 | |
| Nmax | N2:350; CO2: 300 |
| Unit Cell Replication (Nx, Ny, Nz) | (2,2,2) |
| Cubic Box Dimensions (A) | 34.023240 |
| Simulation MOF Mass (amu) | 21846.91 |
| MOF Forcefield, Reference | Snurr [16] |
| FEASST MOF Particle | data.ZIF8_Snurr_rep222 |
The result of each simulation is the PNPD and average potential energy (for each N state). The PNPD may be used to compute the adsorption isotherm by the histogram-reweighting procedure described by Shen and Errington [8]. All systems were single phase and, hence, no phase decomposition of the PNPD was necessary.
The pressure for a particular chemical potential pair was determined from TMMC simulations of the bulk N2/CO2 fluid at the same cutoff.
Results: ZIF-8
Temperature = 300K
Credit:
NIST
|
Credit:
NIST
|
Temperature = 350 K
Credit:
NIST
|
Credit:
NIST
|
Data Availability
Various data files used to generate the reference isotherms are available in a Git Repository: https://github.com/dwsideriusNIST/NIST_SRSW_Data/tree/master/N2_CO2_REF_ISOTHERMS
Files in the repository include:
FEASST particle file for the MOF material [includes atomic coordinates and the forcefield parameters]
FEASST particle files for TraPPE N2 and CO2
Particle number probability distributions for the adsorbed fluid mixture
Isotherm data files, including the individual species adsorption isotherms and selectivity and estimated uncertainties, formatted as AIF files [17]
References
- J. R. Errington, J. Chem. Phys. 118, 9915 (2003).
- M. P. Allen and D. J. Tildesley, Computer Simulation of Liquids (Oxford University Press, New York, 1989).
- D. Frenkel and B. Smit, Understanding Molecular Simulation, 2nd ed. (Academic, San Diego, 2002)., pp.37-38.
- J. R. Errington and A. Z. Panagiotopoulos, J. Chem. Phys., 109, 1093 (1998).
- J. R. Errington and V. K. Shen, J. Chem. Phys., 123, 164103 (2005).
- V. K. Shen and D. W. Siderius, J. Chem. Phys., 140, 244106, 2014.
- V. K. Shen and J. R. Errington, JPC B 108, 19595, 2004.
- V. K. Shen and J. R. Errington, JCP 122, 064508, 2005.
- V. K. Shen, R. D. Mountain, and J. R. Errington, JPC B 111, 6198, 2007.
- D. W. Siderius and V. K. Shen, JPC C 117, 5681, 2013.
- J. A. Potoff and J. I. Siepmann, AIChE J., 47, 1676–1682, 2001.
- CODATA Internationally recommended 2018 values of the Fundamental Physical Constants
- T. J. H. Vlugt, M. G. Martin, B. Smit, J. I. Siepmann, and R. Krishna, Mol Phys, 94, 727, 1998.
- H. W. Hatch, N. A. Mahynski, and V. K. Shen J Res Natl Inst Stan, 123, 123004, 2018.
- E. I. Todorov and W. Smith, The DL\_POLY User Manual (version 4.03).
- H. Zhang and R. Q. Snurr, JPC C, 121, 24000, 2017.
- J. D. Evans, V. Bon, I. Senkovska, S. Kaskel, Langmuir, 37, 4222, 2021.