We report an investigation of water adsorption in the hydrophobic metal-organic framework Al(OH)(1,4-naphthalenedicarboxylate) by means of molecular simulation. We show how simple molecular models allow us to reproduce the experimental isotherm, and how grand canonical Monte Carlo simulations can help elucidate the question of the thermodynamic nature of the adsorption transition, which turns out to be a continuous transition, though the experimental isotherm is quite steep. Moreover, we study the influence of functionalisation of the MOF organic linkers on the hydrophobicity of the material and the nature of the adsorption transition, and explain it in terms of the liquid-vapour phase diagram of water in this family of materials.

SiO is the dominant silicon bearing molecule in the circumstellar medium; however, it agglomerates to form oxygen-rich silicates. Here we present a synergistic effort combining experiments in beams with theoretical investigations to examine mechanisms for this oxygen enrichment. The oxygen enrichment may proceed via two processes, namely, (1) chemically driven compositional separation in (SiO)(n) motifs resulting in oxygen-rich and silicon-rich or pure silicon regions, and (2) reaction between Si(n)O(m) clusters leading to oxygen richer and poorer fragments. While SiO(2) molecules are emitted in selected chemical reactions, they readily oxidize larger Si(n)O(n) clusters in exothermic reactions and are not likely to agglomerate into larger (SiO(2))(n) motifs. Theoretically calculated optical absorption and infrared spectra of Si(n)O(m) clusters exhibit features observed in the extended red emissions and blue luminescence from interstellar medium, indicating that the Si(n)O(m) fragments could be contributing to these spectra.

We report the results of a benchmarking study on hybrid, hybrid-meta, long-range-corrected, meta-generalized gradient approximation (meta-GGA), and GGA density functional theory (DFT) methods for aluminum (Al) clusters. A range of DFT functionals, such as B3LYP, B1B95, PBE0, mPW1PW91, M06, M06-2X, ωB97X, ωB97XD, TPSSh, BLYP, PBE, mPWPW91, M06-L, and TPSS, have been used to optimize the molecular structures and calculate the vibrational frequencies and four energetic parameters for neutral and anionic Al(n) (n = 2-10) clusters. The performances of these functionals are assessed systematically by calculating the vertical ionization energy for neutral Al clusters and the vertical electron detachment energy for anionic Al clusters, along with the cohesive energy and dissociation energy. The results are compared with the available experimental and high-level ab initio calculated results. The calculated results showed that the PBE0 and mPW1PW91 functionals generally provide better results than the other functionals studied. TPSS can be a good choice for the calculations of very large Al clusters. On the other hand, the B3LYP, BLYP, and M06-L functionals are in poor agreement with the available experimental and theoretical results. The calculated results suggest that the hybrid DFT functionals like B3LYP do not always provide better performance than GGA functionals.

Herein a performance assessment of density functionals used for calculating the structural and energetic parameters of bi- and trimetallic Ru-containing organometallic complexes has been performed. The performance of four popular relativistic effective core potentials (RECPs) has also been assessed. On the basis of the calculated results, the MN12-SX (range-separated hybrid functional) demonstrates good performance for calculating the molecular structures, while MN12-L (local functional) performs well for calculating the energetics, including that of the Ru-Ru bond breaking process. The choice of appropriate density functional is a crucial factor for calculating the energetics. The LANL08 demonstrates the lowest performance of the RECPs for calculating the molecular structures, especially the Ru-Ru bond length.

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We report an investigation by means of adsorption experiments and molecular simulation of the behavior of a recently synthesized cationic metal-organic framework. We used a combination of quantum chemistry calculations and classical, forcefield-based Grand Canonical Monte Carlo simulations to shed light into the localization of extra-framework halogenide anions in the material. We also studied the adsorption of small gas molecules into the pores of the material using molecular simulation, and investigated the coadsorption of binary gas mixtures.

We report the results of a benchmarking study on generalized gradient approximation (GGA), meta-GGA, hybrid GGA, and hybrid meta-GGA density functional theory (DFT) methods for 3d transition metal mononitrides (3d-TMNs). The selected DFT functionals are, B97-D, BLYP, BP91, MPW91, PBE96, PW91, M06-L, B3LYP, B97, BHandH, PBE0, M05, M05-2X, M06, M06-2X, M06-HF and TPSSh. The performances of these DFT functionals are assessed by calculating the bond distance, harmonic vibrational frequency and atomization energy of 3d-TMNs. The results are compared with the available experimental and high-level ab initio results. The calculated results show that MPW91, M06-L, and B3LYP functionals provide better results than the other functionals that are taken in this study. In general, the functionals with significant Hartree-Fock exchange show poor performance in most of the 3d-TMNs. Hence, these functionals are not recommended for the studies of structure and energetics in 3d-TMNs. accuracy of multireference methods and less computation time. Generally, DFT methods act as an alternative to high cost ab initio methods. Because of very moderate overall O(N 2 ) scaling, they are computationally less expensive. From the literature, it can be noted that the DFT calculations were also performed on 3d Transition metal mononitrides (3d-TMNs). For instance, Daoudi et al. have performed both ab initio and DFT calculations on ScN. 24 They concluded that DFT methods are accurate but yield higher vibrational frequencies. Later, Chaudhari and Lee studied 3d-TMNs using B3LYP method and concluded that binding energies of 3d-metal mononitrides are higher than monocarbides and monoxides. 25 Even though plenty of experimental and theoretical studies on 3d-TMNs were reported in the literature, a satisfactory description of their electronic, structural, and elastic properties is still an area of active research.In the recent past, an enormous amount of exchange-correlation functionals developed within the DFT framework. Because of this, one needs to pay careful attention to the selection of functionals to study a particular atomic or molecular system. It is widely believed that B3LYP yields a better result in organic systems. In the case of inorganic systems, the selection of DFT functionals is a challenging one. Because metals possess near degenerate energy levels, subsequently these methods show difficulty in determining the ground state of a system. Hence, in order to find out suitable DFT functional, one needs to perform a benchmark study of DFT functionals on these systems. From the literature survey, it can be understood that no systematic DFT assessment study performed on 3d-TMNs, in particular, using recently developed DFT functionals and Minnesota functionals. Earlier, Wu has investigated the structure and energetic properties of 3d-TMNs using DFT methods. From this investigation, it was concluded that the calculated properties are highly dependent on the DFT functionals. 26 But, they selected very few DFT functionals for the study. Apart fr...

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