Dynamic Heterogeneity and Ionic Conduction in an Organic Ionic Plastic Crystal and the Role of Vacancies

Dynamic heterogeneity was investigated for the first time in a conductive organic ionic plastic crystal by molecular dynamics simulation. A minority fraction of ions that possess above-average dynamics were identified in the plastic crystal phase. The signature of this unusual motional behavior is found in the significant increase in the non-Gaussian parameter α­(<i>t</i>). A study by incorporation of vacancies into the crystal structure shows explicit evidence of coexistence of mobile species with an otherwise rigid matrix, which particularly supports the previous explanation on heterogeneous motional narrowing in nuclear magnetic resonance. It is also found that the origin of dynamic heterogeneity here is inseparable from the inherent structural characteristics of organic ions. This work reveals the profound effect brought by heterogeneous dynamics on the conduction mechanism of this material, as well as the important role of defects on ions dynamics

Dynamic Heterogeneity and Ionic Conduction in an Organic Ionic Plastic Crystal and the Role of Vacancies

Dynamic heterogeneity was investigated for the first time in a conductive organic ionic plastic crystal by molecular dynamics simulation. A minority fraction of ions that possess above-average dynamics were identified in the plastic crystal phase. The signature of this unusual motional behavior is found in the significant increase in the non-Gaussian parameter α­(<i>t</i>). A study by incorporation of vacancies into the crystal structure shows explicit evidence of coexistence of mobile species with an otherwise rigid matrix, which particularly supports the previous explanation on heterogeneous motional narrowing in nuclear magnetic resonance. It is also found that the origin of dynamic heterogeneity here is inseparable from the inherent structural characteristics of organic ions. This work reveals the profound effect brought by heterogeneous dynamics on the conduction mechanism of this material, as well as the important role of defects on ions dynamics

Free Energy Calculations for Identifying Efficient Promoter Molecules of Binary sH Hydrogen Clathrates

To determine the stabilizing effect of different promoter molecules on the clathrate, the Gibbs free energy of fully occupied binary sH hydrogen clathrates with secondary guest molecules in the large cages is calculated with Monte Carlo simulations. The small and medium cages of sH are occupied by one H₂ guest molecule. Various promoter molecules enclathrated in the large cages are considered. Simulations are conducted in the pressure range of 250–1000 atm for temperatures ranging from 233 to 273 K. We investigate the effect of dipole moment and molecular size on the thermodynamic stability of sH hydrogen clathrate hydrate

Monte Carlo Calculations of the Free Energy of Binary SII Hydrogen Clathrate Hydrates for Identifying Efficient Promoter Molecules

The thermodynamics of binary sII hydrogen clathrates with secondary guest molecules is studied with Monte Carlo simulations. The small cages of the sII unit cell are occupied by one H₂ guest molecule. Different promoter molecules entrapped in the large cages are considered. Simulations are conducted at a pressure of 1000 atm in a temperature range of 233–293 K. To determine the stabilizing effect of different promoter molecules on the clathrate, the Gibbs free energy of fully and partially occupied sII hydrogen clathrates are calculated. Our aim is to predict what would be an efficient promoter molecule using properties such as size, dipole moment, and hydrogen bonding capability. The gas clathrate configurational and free energies are compared. The entropy makes a considerable contribution to the free energy and should be taken into account in determining stability conditions of binary sII hydrogen clathrates