Solution and nanoscale structure selection: implications for the crystal energy landscape of tetrolic acid

The zeolitic imidazolate frameworks ZIF-8 and ZIF-67 harbour a series of fascinating stimuli responsive properties. Looking at their responsitivity to hydrostatic pressure as stimulus, open questions exist regarding the isotropic compression with non-penetrating pressure transmitting media. By applying a state-of-the-art high-pressure powder X-ray diffraction setup, we revisit the high-pressure behaviour of ZIF-8 and ZIF-67 up to p = 0.4 GPa in small pressure increments. We observe a drastic, reversible change of high-pressure powder X-ray diffraction data at p = 0.3 GPa, discovering large volume structural flexibility in ZIF-8 and ZIF-67. Our results imply a shallow underlying energy landscape in ZIF-8 and ZIF-67, an observation that might point at rich polymorphism of ZIF-8 and ZIF-67, similar to ZIF-4(Zn).

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Revisiting the High-Pressure Properties of the Metal-Organic Frameworks ZIF-8 and ZIF-67

10.26434/chemrxiv.13146278 ◽

2020 ◽

Author(s):

Pia Vervoorts ◽

Stefan Burger ◽

Karina Hemmer ◽

Gregor Kieslich

Keyword(s):

High Pressure ◽

State Of The Art ◽

Energy Landscape ◽

Structural Flexibility ◽

Zeolitic Imidazolate Frameworks ◽

Stimuli Responsive ◽

X Ray Diffraction ◽

X Ray ◽

Open Questions ◽

Metal Organic

The zeolitic imidazolate frameworks ZIF-8 and ZIF-67 harbour a series of fascinating stimuli responsive properties. Looking at their responsitivity to hydrostatic pressure as stimulus, open questions exist regarding the isotropic compression with non-penetrating pressure transmitting media. By applying a state-of-the-art high-pressure powder X-ray diffraction setup, we revisit the high-pressure behaviour of ZIF-8 and ZIF-67 up to p = 0.4 GPa in small pressure increments. We observe a drastic, reversible change of high-pressure powder X-ray diffraction data at p = 0.3 GPa, discovering large volume structural flexibility in ZIF-8 and ZIF-67. Our results imply a shallow underlying energy landscape in ZIF-8 and ZIF-67, an observation that might point at rich polymorphism of ZIF-8 and ZIF-67, similar to ZIF-4(Zn).

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Further Evidence for Energy Landscape Flattening in the Superionic Argyrodites Li6+xP1−xMxS5I (M = Si, Ge, Sn)

10.26434/chemrxiv.8109506.v2 ◽

2019 ◽

Author(s):

Saneyuki Ohno ◽

Bianca Helm ◽

Till Fuchs ◽

Georg Dewald ◽

Marvin Kraft ◽

...

Keyword(s):

Solid State ◽

Activation Barrier ◽

Energy Landscape ◽

General Mechanism ◽

Ionic Conductors ◽

Energy Storage Devices ◽

Ion Conductor ◽

Storage Devices ◽

Open Questions ◽

Sudden Decrease

All-solid-state batteries are promising candidates for next-generation energy storage devices. Although the list of candidate materials for solid electrolytes has grown in the past decade, there are still many open questions concerning the mechanisms behind ionic migration in materials. In particular, the lithium thiophosphate family of materials has shown very promising properties for solid-state battery applications. Recently, the Ge-substituted Li6PS5I argyrodite was shown to be a very fast Li-ion conductor, despite the poor ionic conductivity of the unsubstituted Li6PS5I. Therein, the conductivity was enhanced by over three orders of magnitude due to the emergence of I−/S2−exchange, i.e.site-disorder, which led to a sudden decrease of the activation barrier with a concurrent flattening of the energy landscapes. Inspired by this work, two series of elemental substitutions in Li6+xP1−xMxS5I (M= Si and Sn) were investigated in this study and compared to the Ge-analogue. A sharp reduction in the activation energy was observed at the same M4+/P5+composition as previously found in the Ge-analogue, suggesting a more general mechanism at play. Furthermore, structural analyses with X-ray and neutron diffraction indicate that similar changes in the Li-sublattice occur despite a significant variation in the size of the substituents, suggesting that in the argyrodites, the lithium substructure is most likely influenced by the occurring Li+– Li+interactions. This work provides further evidence that the energy landscape of ionic conductors can be tailored by inducing local disorder.

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Determination of Base Flipping Free Energy Landscapes from Nonequilibrium Stratification

10.26434/chemrxiv.7376081 ◽

2019 ◽

Author(s):

Xiaohui Wang ◽

Zhaoxi Sun

Keyword(s):

Free Energy ◽

Energy Landscape ◽

Sampling Technique ◽

Umbrella Sampling ◽

Energy Simulation ◽

Nonlinear Dependence ◽

Free Energy Landscape ◽

Convergence Criterion ◽

Base Flipping ◽

Convergence Behavior

Correct calculation of the variation of free energy upon base flipping is crucial in understanding the dynamics of DNA systems. The free energy landscape along the flipping pathway gives the thermodynamic stability and the flexibility of base-paired states. Although numerous free energy simulations are performed in the base flipping cases, no theoretically rigorous nonequilibrium techniques are devised and employed to investigate the thermodynamics of base flipping. In the current work, we report a general nonequilibrium stratification scheme for efficient calculation of the free energy landscape of base flipping in DNA duplex. We carefully monitor the convergence behavior of the equilibrium sampling based free energy simulation and the nonequilibrium stratification and determine the empirical length of time blocks required for converged sampling. Comparison between the performances of equilibrium umbrella sampling and nonequilibrium stratification is given. The results show that nonequilibrium free energy simulation is able to give similar accuracy and efficiency compared with the equilibrium enhanced sampling technique in the base flipping cases. We further test a convergence criterion we previously proposed and it comes out that the convergence behavior determined by this criterion agrees with those given by the time-invariant behavior of PMF and the nonlinear dependence of standard deviation on the sample size.

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