David Bousquet : Comment en êtes-vous venu à vous intéresser aux musiques « ethniques » des États-Unis ? Claude Chastagner : Ce n’est pas à distance, ce n'est pas hors du pays, c'est vraiment en ...étant aux États-Unis que j’ai rencontré ces musiques. C’est en travaillant au Texas à plusieurs reprises que j'ai rencontré les musiques et les musiciens de la communauté mexicaine-américaine. C’est en me déplaçant en Louisiane que j’ai découvert la musique cadienne des Blancs de Louisiane, que je con...
An aqueous glycine solution is studied with ab initio molecular dynamics to investigate the structural aspects of the different solvation shells within the zwitterion and their impact on the infrared ...spectrum. The individual contributions to the total IR spectrum from glycine and solvation water are decomposed systematically using the standard schemes in terms of maximally localized Wannier orbitals to define approximate molecular dipole moments in solution. The IR spectra of the aqueous solution and of the solvated zwitterionic glycine molecule itself are compared to those stemming from neutral glycine in the gas phase and a virtual "isolated" zwitterionic glycine molecule vertically transferred from solution into vacuum. Furthermore, electronic polarization effects due to solute-solvent coupling are discussed in detail for the solute and for the interfacial solvent molecules based on dipole moment distribution functions.
We report a structural and thermodynamic investigation of the phase behavior of Ga(OH,F)-MIL-53, a gallium-based metal–organic framework (MOF) having the MIL-53 topology containing 0.7 wt % fluorine ...bonded to the metal. Despite some small structural differences, especially for the hydrated form, the overall physical chemistry behavior of Ga(OH,F)-MIL-53 is very similar to standard fluorine free Ga-MIL-53 material. A combination of in situ X-ray diffraction, in situ Fourier transform infrared spectroscopy, differential scanning calorimetry, and heat capacity measurements allowed us to establish that Ga(OH,F)-MIL-53 under vacuum (i.e., the empty material) exhibits two stable phases: a nonporous narrow-pore (np) phase favored at low temperature and a large-pore (lp) phase favored at high temperature, accompanied by a huge hysteresis effect. Structure determination of the hydrated material Ga(OH,F)-MIL-53_np_H2O obtained after synthesis, activation, and rehydration was also performed. Density functional theory calculations show that it is not a stable structure of Ga(OH,F)-MIL-53 in the absence of adsorbed water molecules. Instead, this hydrated structure is a swollen variant of the np phase, where the flexible framework has expanded to accommodate water molecules.
We demonstrate here that microporous materials can exhibit softening upon adsorption of guest molecules, at low to intermediate pore loading, in parallel to the pore shrinking that is well-known in ...this regime. This novel and counterintuitive mechanical response was observed through molecular simulations of both model pore systems (such as slit pore) and real metal–organic frameworks. It is contrary to common belief that adsorption of guest molecules necessarily leads to stiffening due to increased density, a fact that we show is the high-loading limit of a more complex behavior: a nonmonotonic softening-then-stiffening.
A mixed quantum-classical formulation is developed for a quantum subsystem in strong interaction with an N-particle environment, to be treated as classical in the framework of a hydrodynamic ...representation. Starting from the quantum Liouville equation for the N-particle distribution and the corresponding reduced single-particle distribution, exact quantum hydrodynamic equations are obtained for the momentum moments of the single-particle distribution coupled to a discretized quantum subsystem. The quantum-classical limit is subsequently taken and the resulting hierarchy of equations is further approximated by various closure schemes. These include, in particular, (i) a Grad-Hermite-type closure, (ii) a Gaussian closure at the level of a quantum-classical local Maxwellian distribution, and (iii) a dynamical density functional theory approximation by which the hydrodynamic pressure term is replaced by a free energy functional derivative. The latter limit yields a mixed quantum-classical formulation which has previously been introduced by I. Burghardt and B. Bagchi, Chem. Phys. 134, 343 (2006).
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