In order to investigate the technical feasibility of crystalline porous silicates as hydrogen storage materials, the self-diffusion of molecular hydrogen in all-silica sodalite is modeled using large-scale classical molecular-dynamics simulations employing full lattice flexibility. In the temperature range of 700-1200 K, the diffusion coefficient is found to range from 1.610(-10) to 1.810(-9) m...

Ionic transport in conventional ionic solids is generally considered to proceed via independent diffusion events or "hops." This assumption leads to well-known Arrhenius expressions for transport coefficients, and is equivalent to assuming diffusion is a Poisson process. Using molecular dynamics simulations of the low-temperature B1, B3, and B4 AgI polymorphs, we have compared rates of ion hopp...

In many systems in condensed matter physics and quantum field theory, first order phase transitions are initiated by the nucleation of bubbles of the stable phase. In homogeneous nucleation theory the nucleation rate Γ can be written in the form of the Arrhenius law: Γ = Ae −Hc. Here H c is the energy of the critical bubble, and the prefactor A can be expressed in terms of the determinant of th...

We carried out a molecular modeling study of an important reaction in the combustion of nitrogen-containing chars, the evolution of nitric oxide, (CNO)!NO+(C*). Density functional theory at the B3LYP level was used to provide potential energy surface information and transition state theory was used to provide temperature dependant rate constants. Desorption of NO from nitrogen-containing carbon...

Decomposition mechanisms, activation barriers, Arrhenius parameters, and reaction kinetics of the novel explosive compounds, 3,4-bis(4-nitro-1,2,5-oxadiazol-3-yl)-1,2,5-oxadiazole (BNFF-1), and 3-(4-amino-1,2,5-oxadiazol-3-yl)-4-(4-nitro-1,2,5-oxadiazol-3-yl)-1,2,5-oxadiazole (ANFF-1) were explored by means of density functional theory with a range of functionals combined with variational trans...

We present a theory of desorption of atoms and molecules from solid surfaces based on a chtssical stochastic diffusion formulation. We obtain a simple rate expression which has the form R = (D,/2n) j(T) exp( D,/k,), where T is the temperature, k is Boltxmann’s constant, 0, is the bond enthalpy, and sd, is the surface-adsorbate vibrational frequency. For atoms j(T) = 1, while for molecules j(T) ...

A major mystery of glass-forming liquids is the non-Arrhenius temperature-dependence of the average relaxation time. This paper brie ̄y reviews the classical phenomenological models for non-Arrhenius behavior ± the free volume model and the entropy model ± and critiques against these models. We then discuss a recently proposed model according to which the activation energy of the average relaxat...

Weak pi hydrogen-bonded solute/solvent complexes are studied with ultrafast two-dimensional infrared (2D-IR) vibrational echo chemical exchange spectroscopy, temperature-dependent IR absorption spectroscopy, and density functional theory calculations. Eight solute/solvent complexes composed of a number of phenol derivatives and various benzene derivatives are investigated. The complexes are for...