Ab initio carbon capture in open-site metal–organic frameworks

Journal name:
Nature Chemistry
Year published:
Published online


During the formation of metal–organic frameworks (MOFs), metal centres can coordinate with the intended organic linkers, but also with solvent molecules. In this case, subsequent activation by removal of the solvent molecules creates unsaturated ‘open’ metal sites known to have a strong affinity for CO2 molecules, but their interactions are still poorly understood. Common force fields typically underestimate by as much as two orders of magnitude the adsorption of CO2 in open-site Mg-MOF-74, which has emerged as a promising MOF for CO2 capture. Here we present a systematic procedure to generate force fields using high-level quantum chemical calculations. Monte Carlo simulations based on an ab initio force field generated for CO2 in Mg-MOF-74 shed some light on the interpretation of thermodynamic data from flue gas in this material. The force field describes accurately the chemistry of the open metal sites, and is transferable to other structures. This approach may serve in molecular simulations in general and in the study of fluid–solid interactions.

At a glance


  1. Interaction energy comparison of force fields with decomposed MP2 and UFF.
    Figure 1: Interaction energy comparison of force fields with decomposed MP2 and UFF.

    a,b, NEMO decomposition of the MP2 energies on the Mg path into repulsive (a) and attractive (b) interactions. The black circles are the MP2 results and the solid lines are the fitted force fields for the various atoms. The red line gives the contribution of Mg. c,d, Comparison of the MP2 repulsive and attractive energies (filled symbols) for the eight different paths with the force-field results (lines). Mg and O paths (c) and C paths (d) are compared with the predictions from UFF (open symbols).

  2. Interaction energy comparison of force field with periodic DFT.
    Figure 2: Interaction energy comparison of force field with periodic DFT.

    a,b, The MOF–CO2 interaction energy is plotted along two different paths that cross the minimum energy configuration of CO2 in Mg-MOF-74: CO2 approaching the open metal site from the centre of the pore (a) and CO2 approaching the open metal site in the C-direction (b). Blue curves are DFT calculations that include van der Waals interactions and red curves are obtained from our force field. Both paths are computed in the periodic system.

  3. Comparison of the experimental and simulated isosteric heats of adsorptions as a function of loading.
    Figure 3: Comparison of the experimental and simulated isosteric heats of adsorptions as a function of loading.

    The loading is plotted as the number of CO2 molecules per open metal site. For an ideal material, for which all metal sites are active, the molecular simulations (blue symbols) predict that one CO2 binds to one open metal site. The black, green and olive symbols give the reported experimental data of Mason et al.11, Dietzel et al.10 and Simmons et al.25, respectively. Red lines indicate the enhancement of the CO2 heat of adsorption caused by cooperative effects and was predicted from the molecular simulations.

  4. Comparison of simulated and experimental adsorption isotherms and Henry coefficients.
    Figure 4: Comparison of simulated and experimental adsorption isotherms and Henry coefficients.

    a,b, Experimental (exp.) and predicted (sim.) adsorption isotherms are shown for CO2 (a) and N2 (b) in Mg-MOF-74. The experimental data of Herm et al.30 or Mason et al.11 are shown by the filled blue circles. The open symbols are the simulation results: the green symbols are the results of using the UFF and the red symbols are from the present force field. At low pressure the adsorption is linear in pressure (the proportionality coefficient is defined as the Henry coefficient). c,d, The Henry coefficients are shown as a function of the temperature for CO2 (c) and N2 (d).

  5. Enhancement of the adsorption of CO2 as a function of loading.
    Figure 5: Enhancement of the adsorption of CO2 as a function of loading.

    In this figure we compare a Langmuir isotherm (red) with the results from GCMC simulations (blue). The parameters of the Langmuir isotherm are obtained from the Henry coefficient from the GCMC simulations and the maximum loading, which is set to one CO2 per Mg site. The difference between these curves (green) indicates the enhancement induced by the presence of other CO2 molecules.

  6. Adsorption isotherms of CO2 in additional frameworks.
    Figure 6: Adsorption isotherms of CO2 in additional frameworks.

    ac, Transferability of the methodology was studied in three additional frameworks: Mg2(dobpdc), which is a material with an extended linker using the same atom types as in the Mg-MOF-74 material (a); Mg-MOF-74 and Zn-MOF-74, in which we tested the transferability of our force field for the metal sites by replacing the Mg by the Zn force field, but keeping the force field for the atoms in the linker identical (b); MOF-5, a material that does not have open metal sites (c). Closed and open symbols represent the experimental and simulation adsorption isotherms, respectively.


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Author information

  1. These authors contributed equally to this work

    • Allison L. Dzubak &
    • Li-Chiang Lin


  1. Department of Chemistry and Supercomputing Institute, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455-0431, USA

    • Allison L. Dzubak &
    • Laura Gagliardi
  2. Department of Chemical and Biomolecular Engineering and Chemistry, University of California, Berkeley, Berkeley, California 94720-1462, USA

    • Li-Chiang Lin,
    • Joseph A. Swisher,
    • Roberta Poloni,
    • Sergey N. Maximoff &
    • Berend Smit
  3. Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    • Jihan Kim,
    • Joseph A. Swisher &
    • Berend Smit
  4. Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    • Roberta Poloni


A.L.D. performed the cluster calculations at the MP2 level and the NEMO decomposition of the interaction energies, R.P. performed the periodic DFT calculations, L-C.L., J.A.S. and J.K. performed the molecular simulations, S.N.M. provided some of the optimized MOF structures, A.L.D. and L-C.L. optimized the force field and B.S. and L.G. conceived the research. A.L.D., L-C.L., B.S. and L.G. co-wrote the manuscript and all the authors discussed the results and commented on the manuscript.

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