Flexoelectric radial polarization of single-walled nanotubes from first-principles

Abstract

Flexoelectricity is the polar response of an insulator to strain gradients such as bending. While the size dependence of this effect makes it weak in bulk systems in comparison to piezoelectricity, it suggests that it plays a bigger role in nanoscale systems such as thin films and nanotubes (NTs). In this paper we demonstrate using first-principles calculations that the walls of carbon nanotubes (CNTs) and transition metal dichalcogenide nanotubes (TMD NTs) are polarized in the radial direction, the strength of the polarization increasing as the size of the NT decreases. For CNTs and TMD NTs with chiral indices $(n,m)$, the radial polarization of the walls $P_R$ starts to diverge below $C(n,m)/a=\sqrt{n^2+nm+m^2}\sim 10$, where $C(n,m)$ is the circumference of the NT and $a$ is the lattice constant of the 2D monolayer. For CNTs, $P_R$ drops to zero above this value but for TMD NTs there is a non-zero polarization above this value, which is an ionic rather than electronic effect. The size dependence of $P_R$ in the TMD NTs is interesting: it increases gradually and reaches a maximum of $P_R\sim 100{\text{C/cm}}^2$ at $C(n,m)/a\sim 15$, then decreases until $C(n,m)/a\sim 10$ where it starts to diverge. Measurements of the radial strain on the chalcogen atoms with respect to the 2D monolayers shows that this polarization is the result of a significantly larger strain on the outer bonds than the inner bonds, but did not offer an explanation for the peculiar size dependence. These results suggest that while the walls of smaller CNTs and TMD NTs are polarized, the walls of larger TMD NTs are also polarized due to a difference in strain on the inner and outer atoms in the walls. This result may prove useful for the application of NTs for screening in liquid or biological systems.

arXiv comment7 pages, 5 figures

References in corpus (29)

• The SIESTA method for ab initio order-N materials simulation
• Efficient index handling of multidimensional periodic boundary conditions
• Optimized norm-conserving Vanderbilt pseudopotentials
• The PseudoDojo: Training and grading a 85 element optimized norm-conserving pseudopotential table
• Computational 2D Materials Database: Electronic Structure of Transition-Metal Dichalcogenides and Oxides
• Linear-scaling ab-initio calculations for large and complex systems
• Strain gradient induced polarization in SrTiO3 single crystals
• Ab initio study of BaTiO3 and PbTiO3 surfaces in external electric fields
• Atomistic determination of flexoelectric properties of crystalline dielectrics
• First-principles theory and calculation of flexoelectricity
• Quantum Flexoelectricity in Low Dimensional Systems
• Towards a bulk theory of flexoelectricity
• First-principles theory of frozen-ion flexoelectricity
• Flexoelectricity from density-functional perturbation theory
• Band alignment at metal/ferroelectric interfaces: insights and artifacts from first principles
• First-principles calculation of the band offset at BaO/BaTiO${}_3$ and SrO/SrTiO${}_3$ interfaces
• Intrinsic bending flexoelectric constants in two-dimensional materials
• Nanoscale Smoothing and the Analysis of Interfacial Charge and Dipolar Densities
• Surface control of flexoelectricity
• C2x: a tool for visualisation and input preparation for Castep and other electronic structure codes
• The PSML format and library for norm-conserving pseudopotential data curation and interoperability
• From Layers to Nanotubes: Transition Metal Disulfides TMS2
• First-principles theory of spatial dispersion: Dynamical quadrupoles and flexoelectricity
• Current-density implementation for calculating flexoelectric coefficients
• Optimal finite-range atomic basis sets for liquid water and ice
• High flexoelectric constants in Janus transition-metal dichalcogenides
• Mapping the energy surface of PbTiO3 in multidimensional electric-displacement space
• Metric-wave approach to flexoelectricity within density-functional perturbation theory
• Analysis of a capped carbon nanotube (CNT) with linear-scaling density-functional theory

Cited by in corpus (6)

• Polar meron-antimeron networks in strained and twisted bilayers
• Direct and converse flexoelectricity in two-dimensional materials
• Theory of polar domains in moiré heterostructures
• Curvature-Controlled Band Alignment Transitions in 1D van der Waals Heterostructures
• Theory of polarization textures in crystal supercells
• Electrically tunable stacking domains and ferroelectricity in moiré superlattices