Fingerprint-Based Detection of Non-Local Effects in the Electronic Structure of a Simple Single Component Covalent System

Behnam Parsaeifard,Deb Sankar De,Stefan Goedecker,Jonas A Finkler

doi:10.3390/condmat6010009

Behnam Parsaeifard, Deb Sankar De + Show 2 more

Open Access

https://doi.org/10.3390/condmat6010009

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Journal: Condensed Matter	Publication Date: Feb 20, 2021
Citations: 10	License type: CC BY 4.0

Affiliation: University of Basel

Abstract

Using fingerprints used mainly in machine learning schemes of the potential energy surface, we detect in a fully algorithmic way long range effects on local physical properties in a simple covalent system of carbon atoms. The fact that these long range effects exist for many configurations implies that atomistic simulation methods, such as force fields or modern machine learning schemes, that are based on locality assumptions, are limited in accuracy. We show that the basic driving mechanism for the long range effects is charge transfer. If the charge transfer is known, locality can be recovered for certain quantities such as the band structure energy.

Highlights

Most approximate chemical simulation schemes are based on a locality assumption
Coupled to density functional-based tight binding (DFTB) [33], we have generated a large number of clusters, with 60 carbon atoms
Energies might for instance be degenerate. If these localised physical properties differ for identical or nearly identical environments, localised physical properties are influenced by long range effects

Summary

Introduction

Most approximate chemical simulation schemes are based on a locality assumption. A local property, such as a local charge distribution, an atomic spin polarization or atomic energy as well as bond lengths are assumed to depend only on a nearby local environment, but not features far away. The locality assumption is very well satisfied in many covalently bonded systems. Insertion of a CH2 monomer into the smallest chain, C2 H6 , gives already an energy gain that agrees to within 10−4 Ha with the asymptotic value of the insertion energy for very long chains [1] This shows that the electrons belonging to this inserted sub-unit no longer “see” the end of the chain. This locality principle has been dubbed “nearsightedness” by Walter Kohn [2,3,4] and he claimed it to be valid nearly universally. We will consider pure carbon systems and show that even in such a simple covalent system, non-local effects play an important role

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