Strain and screening: Optical properties of a small-diameter carbon nanotube from first principles

Carbon nanotubes (CNTs) are a one-dimensional material system with intriguing physical properties that lead to emerging applications. While CNTs are unusually strain resistant compared to bulk materials, their optical-absorption spectrum is highly strain dependent. It is an open question, as to what extent this is attributed to strain-dependent (i) electronic single-particle transitions, (ii) dielectric screening, or (iii) atomic geometries including CNT radii. We use cutting-edge theoretical spectroscopy to explain strain-dependent electronic structure and optical properties of an (8,0) CNT. Quasiparticle effects are taken into account using Hedin's GW approximation and excitonic effects are described by solving a Bethe-Salpeter-equation for the optical polarization function. This accurate first-principles approach allows us to identify an inuence of strain on screening of the Coulomb electron-electron interaction and to quantify the impact on electronic structure and optical absorption of one-dimensional systems. We interpret our thoroughly converged results using an existing scaling relation and extend the use of this relation to strained CNTs: We show that it captures optical absorption with satisfactory accuracy, as long as screening, quasiparticle gap, and effective electron and hole masses of the strained CNT are known.