A comparative ab initio study of neutral and charged kink-solitons on conjugated carbon chains

TL;DR

This study systematically compares neutral and charged kink-solitons in conjugated carbon chains using various ab initio methods, revealing how exchange interactions influence their properties and charge-spin distributions.

Contribution

It provides a comprehensive first-principles analysis of kink-solitons, highlighting the impact of different computational methods on their predicted properties.

Findings

Kink size correlates with the amount of HF exchange in the functional.

Charged kinks show distinct charge and spin density behaviors.

Different ab initio methods yield consistent trends in BLA and energy gaps.

Abstract

The ground state of odd-N polyynic oligomers C_{N}H_{2} features kink-solitons in carbon-carbon bond-length alternation (BLA) patterns. We perform a systematic first-principles computational study of neutral and singly-charged kinks in long oligomers addressing relationships between BLA patterns, electron energy gaps, and accompanying distributions of spin and charge densities, both in vacuum and in the screening solvent environment. A quantitative comparison is made of the results derived with four different ab initio methods: from pure DFT to pure Hartree-Fock (HF) and including two popular hybrid density functionals, B3LYP and BHandHLYP. A clear correlation is demonstrated between the derived spatial extent of kinks and the amount of HF exchange used in the functionals. For charged kinks, we find a substantial difference in the behavior of charge and spin densities.