Reaction rate theory with account of the crystal anharmonicity

TL;DR

This paper extends reaction rate theory in solids by incorporating the effects of discrete breathers caused by anharmonicity, showing how they can significantly enhance reaction rates beyond traditional Arrhenius predictions.

Contribution

It introduces a model accounting for discrete breathers in crystals, quantifying their impact on reaction rates and deriving amplification factors under various conditions.

Findings

Reaction rates are increased due to discrete breathers.

Derived reaction rate amplification factors in thermal equilibrium.

Analyzed breather statistics under irradiation conditions.

Abstract

Reaction rate theory in solids is modified taking into account intrinsic localized modes or discrete breathers (DBs) that can appear in crystals with sufficient anharmonicity resulting in violation of Arrhenius law. Large amplitude oscillations of atoms about their equilibrium positions in the lattice cause local potentials of alternating sign, which are described in terms of time-periodic modulations of the potential barriers for chemical reactions taking place in the vicinity of DBs. The reaction rate averaged over large macroscopic volumes and times including a lot of DBs is increased by a factor that depends on the DB statistics. The breather statistics in thermal equilibrium and in thermal spikes in solids under irradiation with swift particles is considered, and the corresponding reaction rate amplification factors are derived.