Multiscale Simulation Of Gas Adsorption In Microporous Molecular Crystal

Microporous materials are solids containing interconnected pores of less than2nm in size.They are widely used for heterogeneous catalysis, adsorption, separation, gas storage and anumber of emerging technologies. Inspired by the intriguing properties of metal organicframeworks (MOFs), the preparation of porous materials is currently of intense interest. Inaddition to extended networks and frameworks, an alternative way to form porosity is to usediscrete molecules between which there are only non-covalent interactions. BecauseMicroporous Organic Molecular Crystals (MOMCs, sometimes termed “organic zeolites”) donot possess an extended framework with covalent or coordination bonds, they can bedissolved and then reassembled in suitable solvents. On the other hand, the computationalinvestigations of this kind of porous materials are very rare. On the basis of the fact, ourmultiscale simulation including the following aspects:1. Molecular structures and electronic properties were investigated for a series of TPPanalogs containing TTF-like fragments using theoretical methodologies based onPBE0/6-31+G(d,p)//PBE0/6-31G(d,p) and HF/6-31+G(d,p)//PBE0/6-31G(d,p) approaches.Substituting bridge atoms O in TPP with S and NH partially and totally and the side phenylfragments with TTF-like fragments may lead to a series of analogues showing electron–donorstrength comparable or better than the ones for the commonly known electron donors. Inaddition, a new series of candidates for organic superconductors were designed based on theTTF-like substitution of TPP side phenyl fragment and both partial and total O/S (O/NH orS/NH) substitution. More interestingly, they are predicted to combine a good ET–donorstrength and the paddle wheel molecular shape responsible for inclusion adducts formationwith the O/NH substituted analogues showing better electron–donor ability.2. A microporous molecular crystal TTP is proposed to investigate the gas–adsorptionproperty. We have generated high-quality potential energy curves for thiophen ehydrogen,thiophene carbon dioxide, thiophene methane, and thiophene nitrogen complexescomparing the values provided by traditional correlated MP2/CBS and CCSD(T)/CBSmethods and by a DFT approach using TPSS, BP86, and BLYP functionals, augmented withdispersion correction. From the comparison, we have concluded that theDFT D/Aug-cc-pVTZ results are in excellent agreement with those obtained fromCCSD(T)/CBS for the equilibrium distance and the interaction energies. Among the threeselected functionals, TPSS D provided the best results and was used to investigate the vander Waals interaction in large system. We propose a computer-aided material design of anorganic zeolite TTP. Potential energy curves for the host H2, host CO2, host CH4, and host N2complexes were generated at the TPSS D/Aug-cc-pVTZ level. The IE between thehost and the guest molecules was predicted in the increasing order of ho stH2<<host N2<host CH4<host CO2, suggesting that TTP can selectively adsorb CO2/CH4over N2and H2.3. We have performed multiscale computational calculations to investigate theselectivity of N2, CH4, or CO2over H2in microporous organic crystal TTB. Our GCMCsimulations based on the modified force field indicate that the selectivity of N2, CH4, or CO2over H2is in the increasing order of N2/H2<CH4/H2<CO2/H2, which is consistent with theorder of isosteric heats of adsorption. In the first-principle calculations, the results at theTPSS-D/Aug-cc-pVTZ level are in excellent agreement with those obtained fromCCSD(T)/CBS for the interaction energies.. The IEs between the channel and the gasmolecules were predicted in the increasing order of channel-H2, channel-N2<channel-CH4<channel-CO2, which corresponds to the GCMC results.4. For the computation of reliable gas adsorption isotherms in MOMC, a general multiscalesimulation procedure is proposed. The density functional theory based B2PLYP-D3/def2-TZVPPmethod is first validated by CCSD(T)/CBS and then used to produce reference data for fitting aforce field that is subsequently used in Grand-Canonical Monte-Carlo (GCMC) simulations. Anew intermolecular force field vdW3, which is designed particularly for non-covalent interactions,is used to compute interaction potentials for CO2, CH4, N2and Xe in the crystal of TPP. Goodagreement between GCMC simulation results based on these potentials and experimental data foradsorption isotherms and heats of adsorption could be observed in all cases.