Classical Langevin Dynamics for Model Hamiltonians

TL;DR

This paper extends the model Hamiltonian method with Langevin dynamics to study the kinetics of structural transformations in complex materials, incorporating dynamical interactions and enabling dynamic simulations beyond equilibrium properties.

Contribution

It introduces a scheme to include Langevin dynamics in the model Hamiltonian framework, allowing for the study of structural transformation kinetics and dynamical interactions.

Findings

Effective Hamiltonian includes a new term for dynamical interactions.

Method enables simulation of structural transformation dynamics.

Parameters derived from first-principles calculations.

Abstract

We propose a scheme for extending the model Hamiltonian method developed originally for studying the equilibrium properties of complex perovskite systems to include Langevin dynamics. The extension is based on Zwanzig's treatment of nonlinear generalized Langevin's equations. The parameters entering the equations of motion are to be determined by mapping from first-principles calculations, as in the original model Hamiltonian method. The scheme makes possible, in principle, the study of the dynamics and kinetics of structural transformations inaccessible to the original model Hamiltonian method. Moreover, we show that the equilibrium properties are governed by an effective Hamiltonian which differs from that used in previous work by a term which captures the coherent part of the previously ignored dynamical interaction with the omitted degrees of freedom. We describe how the additional information required for the Langevin equations can be obtained by a minor extension of the previous mapping.