Chirality-Dependent Properties of Carbon Nanotubes. Electronic Structure: Optical Dispersion Properties, Hamaker Coefficients and van der Waals - London dispersion interactions

TL;DR

This study uses one-electron theory calculations to analyze the optical dispersion spectra of 64 carbon nanotubes, revealing how chirality and geometry influence van der Waals interactions and dielectric properties across different energy ranges.

Contribution

It introduces a new classification scheme for nanotube optical spectra and provides comprehensive calculations of van der Waals interactions based on these spectra.

Findings

Optical dispersion spectra vary systematically with radius below the zone-folding limit.

Van der Waals spectra remain stable down to small nanotubes within each class.

A new optical dielectric function classification scheme is proposed.

Abstract

Optical dispersion spectra at energies up to 30 eV play a vital role in understanding the chirality-dependent van der Waals London dispersion interactions of single wall carbon nanotubes (SWCNTs). We use one-electron theory based calculations to obtain the band structures and the frequency dependent dielectric response function from 0-30 eV for 64 SWCNTs differing in radius, electronic structure classification, and geometry. The resulting optical dispersion properties can be categorized over three distinct energy intervals (M, pi, and sigma, respectively representing 0-0.1, 0.1-5, and 5-30 eV regions) and over radii above or below the zone-folding limit of 0.7 nm. While pi peaks vary systematically with radius for a given electronic structure type, peaks are independent of tube radius above the zone folding limit and depend entirely on SWCNT geometry. Based on these calculated one-electron dielectric response functions we compute and review Van derWaals - London dispersion spectra, full spectral Hamaker coefficients, and van derWaals - London dispersion interaction energies for all calculated frequency dependent dielectric response functions. Our results are categorized using a new optical dielectric function classification scheme that groups the nanotubes according to observable trends and notable features (e.g. the metal paradox) in the 0-30 eV part of the optical dispersion spectra. While the trends in these spectra begin to break down at the zone folding diameter limit, the trends in the related van derWaals - London dispersion spectra tend to remain stable all the way down to the smallest single wall carbon nanotubes in a given class.