Ab Initio Molecular Dynamics Study of Aqueous Solvation of Ethanol and Ethylene

The structure and dynamics of aqueous solvation of ethanol and ethylene are studied by DFT-based Car-Parrinello molecular dynamics. We did not find an enhancement of the structure of the hydrogen bonded network of hydrating water molecules. Both ethanol and ethylene can easily be accommodated in the hydrogen-bonded network of water molecules without altering its structure. This is supports the conclusion from recent neutron diffraction experiments that there is no hydrophobic hydration around small hydrophobic groups. Analysis of the electronic charge distribution using Wannier functions shows that the dipole moment of ethanol increases from 1.8 D to 3.1 D upon solvation, while the apolar ethylene molecule attains an average dipole moment of 0.5 D. For ethylene, we identified configurations with $\pi$-H bonded water molecules, that have rare four-fold hydrogen-bonded water coordination, yielding instantaneous dipole moments of ethylene of up to 1 D. The results provide valuable information for the improvement of empirical force fields, and point out that for an accurate description of the aqueous solvation of ethanol, and even of the apolar ethylene, polarizable force fields are required.Comment: 15 pages, 10 figures, 4 tables, revtex4, submitted to J. Chem. Phy

Dynamic interplay between defective UiO‐66 and protic solvents in activated processes

UiO-66, composed by Zr-oxide inorganic bricks [Zr-6(mu(3)-O)(4)(mu(3)-OH)(4)] and organic terephthalate linkers, is one of the most studied metal-organic frameworks (MOFs) due to its exceptional thermal, chemical, and mechanical stability. Thanks to its high connectivity, the material can withstand structural deformations during activation processes such as linker exchange, dehydration, and defect formation. These processes do alter the zirconium coordination number in a dynamic way, creating open metal sites for catalysis and thus are able to tune the catalytic properties. In this work, it is shown, by means of first-principle molecular-dynamics simulations at operating conditions, how protic solvents may facilitate such changes in the metal coordination. Solvent can induce structural rearrangements in the material that can lead to undercoordinated but also overcoordinated metal sites. This is demonstrated by simulating activation processes along well-chosen collective variables. Such enhanced MD simulations are able to track the intrinsic dynamics of the framework at realistic conditions

Acidity of edge surface sites of montmorillonite and kaolinite

Peer reviewedPreprin

Influence of a confined methanol solvent on the reactivity of active sites in UiO-66

UiO-66, composed of Zr-oxide bricks and terephthalate linkers, is currently one of the most studied metal-organic frameworks due to its exceptional stability. Defects can be introduced in the structure, creating undercoordinated Zr atoms which are Lewis acid sites. Here, additional BrOnsted sites can be generated by coordinated protic species from the solvent. In this Article, a multilevel modeling approach was applied to unravel the effect of a confined methanol solvent on the active sites in UiO-66. First, active sites were explored with static periodic density functional theory calculations to investigate adsorption of water and methanol. Solvent was then introduced in the pores with grand canonical Monte Carlo simulations, followed by a series of molecular dynamics simulations at operating conditions. A hydrogen-bonded network of methanol molecules is formed, allowing the protons to shuttle between solvent methanol, adsorbed water, and the inorganic brick. Upon deprotonation of an active site, the methanol solvent aids the transfer of protons and stabilizes charged configurations via hydrogen bonding, which could be crucial in stabilizing reactive intermediates. The multilevel modeling approach adopted here sheds light on the important role of a confined solvent on the active sites in the UiO-66 material, introducing dynamic acidity in the system at finite temperatures by which protons may be easily shuttled from various positions at the active sites

Hydration of methanol in water. A DFT-based molecular dynamics study

We studied the hydration of a single methanol molecule in aqueous solution by first-principle DFT-based molecular dynamics simulation. The calculations show that the local structural and short-time dynamical properties of the water molecules remain almost unchanged by the presence of the methanol, confirming the observation from recent experimental structural data for dilute solutions. We also see, in accordance with this experimental work, a distinct shell of water molecules that consists of about 15 molecules. We found no evidence for a strong tangential ordering of the water molecules in the first hydration shell.Comment: 5 pages, 3 figures, submitted to Chemical Physics Letter

Ab initio molecular dynamics study of liquid methanol

We present a density-functional theory based molecular-dynamics study of the structural, dynamical, and electronic properties of liquid methanol under ambient conditions. The calculated radial distribution functions involving the oxygen and hydroxyl hydrogen show a pronounced hydrogen bonding and compare well with recent neutron diffraction data, except for an underestimate of the oxygen-oxygen correlation. We observe that, in line with infrared spectroscopic data, the hydroxyl stretching mode is significantly red-shifted in the liquid. A substantial enhancement of the dipole moment is accompanied by significant fluctuations due to thermal motion. Our results provide valuable data for improvement of empirical potentials.Comment: 14 pages, 4 figures, accepted for publication in Chemical Physics Letter

Waterstofwijk Plan voor waterstof in Hoogeveen

In dit publieke rapport wordt waterstof als een aanvullende mogelijkheid voor verduurzaming van de warmtevoorziening in woonwijken gepresenteerd. Het demonstratieproject Waterstofwijk Hoogeveen dient hierbij als rode draad. Voor andere wijken zal per geval bekeken moeten worden of de waterstofoptie echt past bij de betreffende wijk

High pressure diamond-like liquid carbon

We report density-functional based molecular dynamics simulations, that show that, with increasing pressure, liquid carbon undergoes a gradual transformation from a liquid with local three-fold coordination to a 'diamond-like' liquid. We demonstrate that this unusual structural change is well reproduced by an empirical bond order potential with isotropic long range interactions, supplemented by torsional terms. In contrast, state-of-the-art short-range bond-order potentials do not reproduce this diamond structure. This suggests that a correct description of long-range interactions is crucial for a unified description of the solid and liquid phases of carbon.Comment: 4 pages, 5 figure