Canonical Nonlinearity for Coupled Linear Systems

TL;DR

This paper investigates the complex nonlinearity in substitutional alloys by modeling coupled linear systems and analyzing their behavior through dynamic mode decomposition, revealing dominant modes of structural evolution.

Contribution

It introduces a simplified coupled linear system model to analyze the nonlinearity in alloy structures and identifies key dynamic modes related to structural ordering.

Findings

Two dominant modes capture changes in nonlinearity.

One mode evolves from random to ordered configurations.

Another mode varies around different levels of order.

Abstract

For classical discrete system under constant composition, typically reffered to as substitutional alloys, correspondence between interatomic many-body interactions and structure in thermodynamic equilibrium exhibit profound, complicated nonlinearity (canonical nonlinearity). Our recent studies clarify that the nonlinearity can be reasonablly described both by specially-introduced vector field on configuration space and by corresponding diverngence on statistical manifold. While these studies shown that the correlation between vector field and local contribution to the divergence can be well characterized by coordination number for a set of selected structural degree of freedoms (SDFs), it is unclear whether the correlations between different set of SDFs purely comes from the difference in covariance matrix of CDOS (determined by coordination number) or additional information such as the shape of CP should be further required. To clarify the problem, we here propose simplified model of the so-called Coupled Linear System (CLS), which consists of the m-mixture of the configurational density of states for linear systems. We demonstrate that the CLS can reasonablly capture the changes in the local nonlinearity w.r.t. the changes in coordination number. Through the dynamic mode decomposition on CLS, we elucidate that there exists two dominant modes to capture the changes in the nonlinearity, where the one uniformly evolves from random to ordered configuration, and the another individually evolves around random, partially ordered and ordered configuration.