Computational Chemistry Methods for Nanoporous Materials

International audienceWe present here the computational chemistry methods our group uses to investigate the physical and chemical properties of nanoporous materials and adsorbed fluids. We highlight the multiple time and length scales at which these properties can be examined and discuss the computational tools relevant to each scale. Furthermore, we include the key points to consider—upsides, downsides, and possible pitfalls—for these methods

Pressure promoted low-temperature melting of metal–organic frameworks

International audienceMetal–organic frameworks (MOFs) are microporous materials with huge potential for chemical processes. Structural collapse at high pressure, and transitions to liquid states at high temperature, have recently been observed in the zeolitic imidazolate framework (ZIF) family of MOFs. Here, we show that simultaneous high-pressure and high-temperature conditions result in complex behaviour in ZIF-62 and ZIF-4, with distinct high- and low-density amorphous phases occurring over different regions of the pressure–temperature phase diagram. In situ powder X-ray diffraction, Raman spectroscopy and optical microscopy reveal that the stability of the liquid MOF state expands substantially towards lower temperatures at intermediate, industrially achievable pressures and first-principles molecular dynamics show that softening of the framework coordination with pressure makes melting thermodynamically easier. Furthermore, the MOF glass formed by melt quenching the high-temperature liquid possesses permanent, accessible porosity. Our results thus imply a route to the synthesis of functional MOF glasses at low temperatures, avoiding decomposition on heating at ambient pressure

Modélisation moléculaire des propriétés physico-chimiques de matériaux microporeux

During this PhD, we perform studies based on numerical simulation (Ab initio molecular dynamics for instance) of physico-chemical properties for crystalline adsorbents industrially used, like zeolites,or could be used someday, like hybrid materials or MOFs (Metal–Organic Frameworks). We are primarily interested in adsorption properties of molecular fluids and their mixtures but also in the mechanical and thermal behaviors of nanoporous solids. The aim is to reveal relationships between molecular structures and properties, via multiscale modeling, to construct a rational design approach for such materials.Dans cette thèse, on réalise des études basées sur les méthodes de simulation numérique (Dynamique moléculaire ab initio notamment) des propriétés physico-chimiques des adsorbants cristallins utilisés industriellement, comme les zéolithes,ou qui pourraient l’être dans le futur, comme les matériaux hybrides MOFs (Metal–Organic Frameworks). On s’intéresse en premier lieu aux propriétés d’adsorption des fluides moléculaires et de leurs mélanges, mais aussi au comportement mécanique et thermique des solides nanoporeux. Il s'agit d'expliciter des relations structure-propriétés, par le biais de simulations multi-échelle, pour établir une véritable approche de design rationnel de tels matériaux

Molecular modelling of physics-chemical properties in microporous solids

Dans cette thèse, on réalise des études basées sur les méthodes de simulation numérique (Dynamique moléculaire ab initio notamment) des propriétés physico-chimiques des adsorbants cristallins utilisés industriellement, comme les zéolithes,ou qui pourraient l’être dans le futur, comme les matériaux hybrides MOFs (Metal–Organic Frameworks). On s’intéresse en premier lieu aux propriétés d’adsorption des fluides moléculaires et de leurs mélanges, mais aussi au comportement mécanique et thermique des solides nanoporeux. Il s'agit d'expliciter des relations structure-propriétés, par le biais de simulations multi-échelle, pour établir une véritable approche de design rationnel de tels matériaux.During this PhD, we perform studies based on numerical simulation (Ab initio molecular dynamics for instance) of physico-chemical properties for crystalline adsorbents industrially used, like zeolites,or could be used someday, like hybrid materials or MOFs (Metal–Organic Frameworks). We are primarily interested in adsorption properties of molecular fluids and their mixtures but also in the mechanical and thermal behaviors of nanoporous solids. The aim is to reveal relationships between molecular structures and properties, via multiscale modeling, to construct a rational design approach for such materials

Melting of zeolitic imidazolate frameworks with different topologies: insight from first-principles molecular dynamics

Metal–organic frameworks are chemically versatile materials, and excellent candidates for many applications from carbon capture to drug delivery, through hydrogen storage. While most studies so far focus on the crystalline MOFs, there has been a recent shift to the study of their disordered states, such as defective structures, glasses, gels, and very recently liquid MOFs. Following the publication of the melting mechanism of zeolitic imidazolate framework ZIF-4, we use here molecular simulation in order to investigate the similarities and differences with two other zeolitic imidazolate frameworks, ZIF-8 and ZIF-zni. We perform first principles molecular dynamics simulations to study the melting phenomena and the nature of the liquids obtained, focusing on structural characterization at the molecular scale, dynamics of the species, and thermodynamics of the solid–liquid transition. We show how the retention of chemical configuration, the changes in the coordination network, and the variation of the porous volume in the liquid phase are influenced by the parent crystalline framework.<br /

Contribution a la conception d'une station experimentale pour l'etude du comportement des murs de soutenement

SIGLECNRS TD Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Speeding Up Discovery of Auxetic Zeolite Frameworks by Machine Learning

The characterization of the mechanical properties of crystalline materials is nowadays considered a routine computational task in DFT calculations. However, its high computational cost still prevents it from being used in high-throughput screening methodologies, where a cheaper estimate of the elastic properties of a material is required. In this work, we have investigated the accuracy of force field calculations for the prediction of mechanical properties, and in particular for the characterization of the directional Poisson’s ratio. We analyze the behavior of about 600,000 hypothetical zeolitic structures at the classical level (a scale three orders of magnitude larger than previous studies), to highlight generic trends between mechanical properties and energetic stability. By comparing these results with DFT calculations on 991 zeolitic frameworks, we highlight the limitations of force field predictions, in particular for predicting auxeticity. We then used this reference DFT data as a training set for a machine learning algorithm, showing that it offers a way to build fast and reliable predictive models for anisotropic properties. The accuracies obtained are, in particular, much better than the current “cheap” approach for screening, which is the use of force fields. These results are a significant improvement over the previous work, due to the more difficult nature of the properties studied, namely the anisotropic elastic response. It is also the first time such a large training data set is used for zeolitic materials. </div

Structure of Metal–Organic Framework Glasses by Ab Initio Molecular Dynamics

While metal–organic frameworks have been mostly studied in their crystalline form, recent advances have been made on their amorphous phases, both in fundamental understanding and in relation to possible applications. In particular, the zeolitic imidazolate (ZIF) glasses, that can be obtained from quenching liquid ZIFs, have shown promise. However, the details of their microscopic structure are very hard to probe experimentally. Here we use ab initio molecular dynamics simulations to investigate the nature of the ZIF glasses obtained from quenching molten ZIFs in silico. Through computational modeling of the melt–quench process on three different ZIF crystals, we aim to understand the effect of topology and chemistry upon the structure of the glass, compared to crystalline precursor and high temperature liquid. It is the first direct computational description of MOF glasses at the quantum chemical level. </div

Melting of zeolitic imidazolate frameworks with different topologies: insight from first-principles molecular dynamics

Metal–organic frameworks are chemically versatile materials, and excellent candidates for many applications from carbon capture to drug delivery, through hydrogen storage. While most studies so far focus on the crystalline MOFs, there has been a recent shift to the study of their disordered states, such as defective structures, glasses, gels, and very recently liquid MOFs. Following the publication of the melting mechanism of zeolitic imidazolate framework ZIF-4, we use here molecular simulation in order to investigate the similarities and differences with two other zeolitic imidazolate frameworks, ZIF-8 and ZIF-zni. We perform first principles molecular dynamics simulations to study the melting phenomena and the nature of the liquids obtained, focusing on structural characterization at the molecular scale, dynamics of the species, and thermodynamics of the solid–liquid transition. We show how the retention of chemical configuration, the changes in the coordination network, and the variation of the porous volume in the liquid phase are influenced by the parent crystalline framework.<br

Biofilm formation of the food spoiler Brochothrix thermosphacta on different industrial surface materials using a biofilm reactor

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