Modeling of amorphous carbon structures with arbitrary structural constraints

TL;DR

This paper introduces a simulated annealing-based method to generate amorphous carbon structures with customizable hybridization configurations, enabling detailed study of their physical properties like bulk modulus.

Contribution

The paper presents a novel approach using a tailored Cost Function and simulated annealing to generate amorphous carbon structures with arbitrary constraints, including hybridization segregation.

Findings

Bulk modulus depends on mean coordination following a power law with exponent ~1.51.

Modified Cost Function allows segregation of hybridizations, affecting property correlations.

Generated structures cover nearly all hybridization combinations, enabling comprehensive property analysis.

Abstract

In this paper we describe a method to generate amorphous structures with arbitrary structural constraints. This method employs the Simulated Annealing algorithm to minimize a simple yet carefully tailored Cost Function (CF). The Cost Function is composed of two parts: a simple harmonic approximation for the energy-related terms and a cost that penalizes configurations that do not have atoms in the desired coordinations. Using this approach, we generated a set of amorphous carbon structures spawning nearly all the possible combinations of $sp$, $sp^2$ and $sp^3$ hybridizations. The bulk moduli of this set of amorphous carbons structures was calculated using Brenner's potential. The bulk modulus strongly depends on the mean coordination, following a power law behavior with an exponent $\nu=1.51 \pm 0.17$. A modified Cost Function that segregates carbon with different hybridizations is also presented, and another set of structures was generated. With this new set of amorphous materials, the correlation between the bulk modulus and the mean coordination weakens. This method proposed can be easily modified to explore the effects on physical properties of the presence hydrogen, dangling bonds, and structural features such as carbon rings.