Machine learning using host/guest energy histograms to predict adsorption in metal–organic frameworks: Application to short alkanes and Xe/Kr mixtures

A machine learning (ML) methodology that uses a histogram of interaction energies has been applied to predict gas adsorption in metal–organic frameworks (MOFs) using results from atomistic grand canonical Monte Carlo (GCMC) simulations as training and test data. In this work, the method is first extended to binary mixtures of spherical species, in particular, Xe and Kr. In addition, it is shown that single-component adsorption of ethane and propane can be predicted in good agreement with GCMC simulation using a histogram of the adsorption energies felt by a methyl probe in conjunction with the random forest ML method. The results for propane can be improved by including a small number of MOF textural properties as descriptors. We also discuss the most significant features, which provides physical insight into the most beneficial adsorption energy sites for a given application

Metal-Organic Frameworks with Metal Catecholates for O2/N2 Separation

Oxygen and nitrogen are widely produced feedstocks with diverse fields of applications, but are primarily obtained via the energy-intensive cryogenic distillation of air. More energy-efficient processes are desirable, and materials such as zeolites and metal-organic frameworks (MOFs) have been studied for air separation. Inspired by recent theoretical work identifying metal-catecholates for enhancement of O2 selectivity MOFs, in this work the computation-ready experimental (CoRE) database of MOF structures was screened to identify promising candidates for incorporation of metal catecholates. Based on structural requirements, preliminary Grand-Canonical Monte Carlo simulations, and further constraints to ensure the computational feasibility, over 5,000 structures were eliminated and four MOFs (UiO-66(Zr), Ce-UiO-66, MOF-5, and IRMOF-14) were treated with periodic density functional theory (DFT). Metal catecholates (Mg, Co, Ni, Zn, and Cd) were selected based on cluster DFT calculations and were added to the shortlisted MOFs. Periodic DFT was used to compute O2 and N2 binding energies near metal catecholates. We find that the binding energies are primarily dependent on the metals in the metal catecholates, all of which bind O2 quite strongly (80-258 kJ/mol) and have weaker binding for N2 (3-148 kJ/mol). Of those studied here, Cd-catecholated MOFs are identified as the most promisin

Advances, Updates, and Analytics for the Computation-Ready, Experimental Metal–Organic Framework Database: CoRE MOF 2019

Over 14 000 porous, three-dimensional metal–organic framework structures are compiled and analyzed as a part of an update to the Computation-Ready, Experimental Metal–Organic Framework Database (CoRE MOF Database). The updated database includes additional structures that were contributed by CoRE MOF users, obtained from updates of the Cambridge Structural Database and a Web of Science search, and derived through semiautomated reconstruction of disordered structures using a topology-based crystal generator. In addition, value is added to the CoRE MOF database through new analyses that can speed up future nanoporous materials discovery activities, including open metal site detection and duplicate searches. Crystal structures (only for the subset that underwent significant changes during curation), pore analytics, and physical property data are included with the publicly available CoRE MOF 2019 database

Transferable potentials for phase equilibria. I. United-atom description of n-alkanes

A new set of united-atom Lennard-Jones interaction parameters for n-alkanes is proposed from fitting to critical temperatures and saturated liquid densities. Configurational-bias Monte Carlo simulations in the Gibbs ensemble were carried out to determine the vapor-liquid coexistence curves for methane to dodecane using three united-atom force fields: OPLS [Jorgensen, et al. J. Am. Chem. Soc. 1984, 106, 813], SKS [Siepmann, et al. Nature 1993, 365, 330], and TraPPE. Standard specific densities and the high-pressure equation-ofstate for the transferable potentials for phase equilibria (TraPPE) model were studied by simulations in the isobaric-isothermal and canonical ensembles, respectively. It is found that one set of methyl and methylene parameters is sufficient to accurately describe the fluid phases of all n-alkanes with two or more carbon atoms. Whereas other n-alkane force fields employ methyl groups that are either equal or larger in size than the methylene groups, it is demonstrated here that using a smaller methyl group yields a better fit to the set of experimental data. As should be expected from an effective pair potential, the new parameters do not reproduce experimental second virial coefficients. Saturated vapor pressures and densities show small, but systematic deviation from the experimental data