Redox potentials of aryl derivatives from hybrid functional based first principles molecular dynamics

Acknowledgements We acknowledge the National Science Foundation of China (No. 41222015, 41273074, 41572027 and 21373166), Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund (the second phase), the Foundation for the Author of National Excellent Doctoral Dissertation of P. R. China (No. 201228), Newton International Fellowship Program and the financial support from the State Key Laboratory at Nanjing University. We are grateful to the High Performance Computing Center of Nanjing University for allowing us to use the IBM Blade cluster system. Open access via RSC Gold for GoldPeer reviewedPublisher PD

Acidity constants and redox potentials of uranyl ions in hydrothermal solutions

Acknowledgements We thank Matthias Krack for supplying us with the pseudopotential and basis sets for U. We acknowledge the National Science Foundation of China (No. 41222015, 41273074, 41572027 and 21373166), Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund (the second phase), the Foundation for the Author of National Excellent Doctoral Dissertation of PR China (No. 201228), Newton International Fellowship Program and the financial support from the State Key Laboratory at Nanjing University. We are grateful to the High Performance Computing Center of Nanjing University for allowing us to use the IBM Blade cluster system. Open access via RSC Gold 4 Gold.Peer reviewedPublisher PD

Acidity of edge surface sites of montmorillonite and kaolinite

Peer reviewedPreprin

Acidities of confined water in interlayer space of clay minerals

The acid chemistry of confined waters in smectite interlayers have been investigated with first principles molecular dynamics (FPMD) simulations. Aiming at a systematic picture, we establish the model systems to take account of the three possible controlling factors: layer charge densities (0 e, 0.5 e and 1.0 e per cell), layer charge locations (tetrahedral and octahedral) and interlayer counterions (Na+ and Mg2+). For all models, the interlayer structures are characterized in detail. Na+ and Mg2+ show significantly different hydration characteristics: Mg2+ forms a rigid octahedral hydration shell and resides around the midplane, whereas Na+ binds to a basal oxygen atom and forms a very flexible hydration shell, which consists of five waters on average and shows very fast water exchanges. The method of constraint is employed to enforce the water dissociation reactions and the thermodynamic integration approach is used to derive the free-energy values and the acidity constants. Based on the simulations, the following points have been gained. (1) The layer charge is found to be the direct origin of water acidity enhancement in smectites because the neutral pore almost does not have influences on water dissociations but all charged pores do. (2) With a moderate charge density of 0.5 e per cell, the interlayer water shows a pKa value around 11.5. While increasing layer charge density to 1.0 e, no obvious difference is found for the free water molecules. Since 1.0 e is at the upper limit of smectites’ layer charge, it is proposed that the calculated acidity of free water in octahedrally substituted Mg2+-smectite, 11.3, can be taken as the lower limit of acidities of free waters. (3) In octahedrally and tetrahedrally substituted models, the bound waters of Mg2+ show very low pKa values: 10.1 vs 10.4. This evidences that smectites can also promote the dissociations of the coordinated waters of metal cations. The comparison between the two Mg2+-smectites reveals that different layer charge locations do not lead to obvious differences for bound and free water acidities.<br/

Interlayer structure and dynamics of alkylammonium-intercalated smectites with and without water : A molecular dynamics study

The structure and dynamics of alkylammonium-intercalated smectites were simulated using molecular dynamics employing the clayff-CVFF force field, the reliability of which was firstly validated for these systems. The layering behaviors of alkyl chains confirm the scenarios of the monolayer, transition and bilayer configurations for short, medium-length and long carbon tails, respectively. In the systems without water, the alkylammonium groups are all anchored firmly above the surface six-member rings through H bonds between ammonium hydrogen and surface oxygen, and the alkyl tails are a little more mobile. With water involved, some ammoniums are dragged out of the potential barriers of the six-member rings by water molecules through the strong H bonds between water oxygen and ammonium hydrogen. The intercalated water scarcely affects the basal spacing, alkyl chain layering or alkylammonium dynamics. It is also found that the systems with alkyl chains of 11 to 14 exhibit the greatest density, resulting in the extremely limited mobility of the intercalated species

Spatial-Temporal Change and Synergy/Trade-Off Relationship of &ldquo;Production&ndash;Living&ndash;Ecological&rdquo; Space along the Sino-Vietnamese Border

The internal trade-off of land space is caused by the competition of land use for multiple functions, such as agricultural production, economic development and ecological protection. In response to this common problem, this study uses a positive and negative assignment method and a more refined evaluation scale to analyze the spatial and temporal variation characteristics and synergy/trade-off relationship of production&ndash;living&ndash;ecological space in the Sino-Vietnamese border area from 2000 to 2020. The results show that: (1) There was great regional diversity in the evolution characteristics of the Sino-Vietnamese border. Production space (PS) and living space (LS) presented prominent expansion, and ecological space (ES) was shrinking. (2) From 2000 to 2020, the degree of synergy between PS and LS has increased gradually. The trade-off relationship between PS and ES has shown different fluctuation intensities. The synergy/trade-off relationship between LS and ES has changed, and its trade-off intensity has continuously increased. (3) On the spatial scale, the PS and LS trade-off areas are mostly distributed in the central and western regions with higher altitudes, and the spatial pattern of the synergy zone is expanding. The synergy and trade-off relationship between PS and ES are relatively stable over time. The area of the trade-off between LS and ES has expanded gradually. In conclusion, the synergy/trade-off relationship between the PLES functions has strong consistency with regional economic and social development, which can serve as a scientific basis for the healthy and sustainable development of land space

First-principles molecular dynamics insight into Fe2+ complexes adsorbed on edge surfaces of clay min

Using first-principles molecular-dynamics simulations, probable inner-sphere complexes of Fe adsorbed on the edge surfaces of clay minerals were investigated. Ferrous ions are important reductants in natural processes and their properties can be altered significantly by complexation on edge surfaces of clay minerals. However, the microscopic picture of adsorption sites and structures of Fe is difficult to reveal with modern experimental techniques and, therefore, remains unclear. From the results of first-principles molecular-dynamics simulations, evidence has been provided that complexes on:Si-O sites were the most stable forms, which should be responsible for the experimentally observed pHdependent uptake. Such complexation was found to be strong enough to distort the local coordination structures of Si-O tetrahedra in the substrate. Analyses showed that Fe-O coordination structures were dominated by the solvent with surface groups participating in the complexes via H bonding. The present study provided a microscopic basis for understanding the chemical processes involving surfacecomplexed Fe ions