The development of computational methods to explore crystalline materials has received significant attention in the last decades. Different codes have been reported to help researchers to evaluate and learn about the structure of materials and to understand and predict their properties. In this Methods article, we present an updated version of PoreBlazer, an openaccess, open-source Fortran 90 code to calculate structural properties of porous materials. The article describes the properties calculated by the code, their physical meaning, and their relationship to the properties that can be measured experimentally. Here, we reflect on the methods in the code and discuss features of the most recent version. First, we demonstrate the capabilities of PoreBlazer on the prototypical metal−organic framework (MOF) materials, HKUST-1, IRMOF-1, and ZIF-8, and compare the results to those obtained with other codes, Zeo++ and RASPA. Second, we apply PoreBlazer to the recently assembled database of MOF materialsthe CSD MOF subsetand compare properties such as the accessible surface area and pore volume from PoreBlazer and the two other codes, and reflect on the possible sources of the differences. Finally, we use PoreBlazer to illustrate how correlations between various structural characteristics can be mined using interactive, dynamic data visualization and how material informatics approachesincluding principal component analysis and machine learningcan accelerate the discovery of new materials and new functionalities. The results of these calculations, along with the PoreBlazer code, documentation, and case studies, are

Ge substitution for Si in zeolites containing double-four-membered rings is far more complex than thought.

Large-scale targeted exploration of metal–organic frameworks (MOFs) with characteristics such as specific surface chemistry or metal-cluster family has not been investigated so far.

The low coverage adsorption properties of alkanes, alkenes, and aromatics of the linear, branched, and cyclic type (ca. 70 molecules) were studied using inverse pulse gas chromatography at zero coverage on the zirconium metal− organic framework UiO-66 and its functionalized analogues UiO-66-Me, UiO-66-NO 2 , UiO-66-Me 2 in the temperature range 433−573 K. In our study, we determined and analyzed the adsorption enthalpy, Henry constants, and entropic factors. Preferential adsorption of bulky molecules is observed with specific adsorbate and cage size effects, yielding very specific, preferential adsorption. Remarkably high adsorption selectivity factors (up to 14) for cyclo-compared to nalkanes were found. The presence of additional groups (methyl, nitro) on the linkers in the framework influences adsorption properties significantly, mainly by reducing the effective pore size. Whereas increased selectivity is observed for UiO-66-Me, this effect decreases again upon addition of a second methyl group, UiO-66-Me 2 . The latter allows for tuning confinement factors inside the pores, thus adsorption properties of the metal−organic framework. The selective adsorption results from the interaction in the smallest octahedral cage. The extreme confinement in the tetrahedral cage allows for stereoselective separation of disubstituted cycloalkanes and cis/trans alkenes. Monte Carlo simulations were performed for the unfunctionalized UiO-66 framework. First, a comparative study between the force fields Dreiding and UFF is performed with n-alkanes to obtain accurate and reproducible values. The simulations show adsorbate molecular size−adsorbent cage size effects similar to window/cage effects reported for zeolites (e.g., silicalite). Second, adsorption properties were simulated for selected cases, including stereoisomers. Careful analysis of the adsorbate's molecular positioning in the framework confirms the experimental data. The framework's selectivity results from adsorption in the tetrahedral cage at zero coverage. Furthermore, simulations show important contributions of entropic factors to the observed adsorption selectivity.

Atomic partial charges are parameters of key importance in the simulation of Metal-Organic Frameworks (MOFs), since Coulombic interactions decrease with the distance more slowly than van der Waals interactions. But despite its relevance, there is no method to unambiguously assign charges to each atom, since atomic charges are not quantum observables. There are several methods that allow the calculation of atomic charges, most of them starting from the wavefunction or the electronic density or the system, as obtained with quantum mechanical calculations. In this work, we describe the most common methods employed to calculate atomic charges in MOFs. In order to show the influence that even small variations of structure have on atomic charges, we present the results that we obtained for DMOF-1. We also discuss the effect that small variations of atomic charges have on the predicted structural properties IRMOF-1. arXiv:1802.08771v1 [cond-mat.mtrl-sci]

Controlling thermal expansion is an important, not yet resolved, and challenging problem in materials research. A conceptual design is introduced here, for the first time, for the use of metal–organic frameworks (MOFs) as platforms for controlling thermal expansion devices that can operate in the negative, zero, and positive expansion regimes. A detailed computer simulation study, based on molecular dynamics, is presented to support the targeted application. MOF-5 has been selected as model material, along with three molecules of similar size and known differences in terms of the nature of host–guest interactions. It has been shown that adsorbate molecules can control, in a colligative way, the thermal expansion of the solid, so that changing the adsorbate molecules induces the solid to display positive, zero, or negative thermal expansion. We analyze in depth the distortion mechanisms, beyond the ligand metal junction, to cover the ligand distortions, and the energetic and entropic effect on the thermo-structural behavior. We provide an unprecedented atomistic insight on the effect of adsorbates on the thermal expansion of MOFs as a basic tool toward controlling the thermal expansion.

A tutorial review for mining the ever growing number of metal–organic frameworks data in the Cambridge Structural Database, for MOF scientists of all backgrounds.

Infrared spectra (IR) of a great variety of zeolite frameworks in the limit of pure silica composition are calculated by molecular dynamics and also recorded experimentally. This enables us to study and assess the effect of three flexible force fields from the literature developed for zeolites in reproducing the IR spectra: the force fields by Demontis (J. Phys. Chem. 1988, 92, 867), Nicholas (J. Am. Chem. Soc. 1991, 113, 4792), and Hill (J. Phys. Chem. 1995, 99, 9536). On one side, a qualitative comparison is undertaken; on the other, a similarity index is introduced to perform a quantitative assessment of the similarity of spectra. It is applied to experimental spectra and enables us to arrange the frameworks in three different sets. It can also be applied to study the agreement of the spectra obtained with the three force fields with experimental spectra on a quantitative basis. The force field by Nicholas performs best, followed by the force field by Demontis. Frameworks are therefore analyzed purely theoretically with the Nicholas force field to investigate the dependency on frameworks. This yields a new classification in sets, which is found to be related to the topology of the frameworks. Surprisingly, these sets do not agree with the sets obtained with experimental spectra. As a consequence, it is found that none of the force fields is good enough to enable the identification of frameworks based on their experimental spectra. In a comparison of spectra generated by different force fields, it is found that the Nicholas and Hill force fields generate the most similar IR spectra. ■ INTRODUCTIONZeolites are a class of compounds of great industrial and natural importance made of frameworks of high regularity and beauty. When trying to understand and model these frameworks in order to reproduce some of their physicochemical properties, they are normally considered rigid for simplicity and for reasons of computational cost. However, these frameworks vibrate, giving rise to IR and Raman spectra, 1 where some of the bands are sensitive to details of the structure and to the Si/Al ratio. Therefore, IR and Raman techniques are often used in the characterization of the structures under study. But flexibility is also important in the industrially important diffusion processes, since it favors intermittent opening of the windows. 2ab And from the computational point of view, IR spectroscopy is a good probe to validate force fields that are intended at reproducing changes in phase of the host molecules or other structural changes.Siliceous zeolites, although consisting of only two types of atoms and a single type of bond (the Si−O single bond), exhibit nevertheless a surprising variety of frameworks. These differ in their symmetry properties, both locally through the choice and combination of so-called Secondary Building Units (SBUs) and in their space groups, the dimensionality of channels for suitable host molecules, their overall porosity and pore size, etc. The frameworks selected in this study are representative m...