Probe Type II Band Alignment in One-Dimensional Van Der Waals Heterostructures Using First-Principles Calculations

Summary

Calculations performed by the Vienna Ab initio Simulation Package can be used to identify the intrinsic electronic properties of nanoscale materials and predict the potential water-splitting photocatalysts.

Abstract

Computational tools based on density-functional theory (DFT) enable the exploration of the qualitatively new, experimentally attainable nanoscale compounds for a targeted application. Theoretical simulations provide a profound understanding of the intrinsic electronic properties of functional materials. The goal of this protocol is to search for photocatalyst candidates by computational dissection. Photocatalytic applications require suitable band gaps, appropriate band edge positions relative to the redox potentials. Hybrid functionals can provide accurate values of these properties but are computationally expensive, whereas the results at the Perdew-Burke-Ernzerhof (PBE) functional level could be effective for suggesting strategies for band structure engineering via electric field and tensile strain aiming to enhance the photocatalytic performance. To illustrate this, in the present manuscript, the DFT based simulation tool VASP is used to investigate the band alignment of nanocomposites in combinations of nanotubes and nanoribbons in the ground state. To address the lifetime of photogenerated holes and electrons in the excited state, nonadiabatic dynamics calculations are needed.

Introduction

The worldwide demand for clean and sustainable energy has spurred research for promising materials to reduce dependence on finite petroleum resources. Simulations are more efficient and economical than experiments in accelerating the search for new functional materials¹. Material design from a theoretical perspective^2,3,4 is now more and more popular due to rapid advances in computational resources and theory developments, making computational simulations more reliable⁵. The density functional theory (DFT) calculations implement....

Protocol

1. Optimize the atomic structure.

1. Prepare four input files for structure relaxation calculation by VASP: INCAR, POSCAR, POTCAR, and KPOINTS.
   NOTE: There are specified parameters in the INCAR file that define the calculation. The line "EDIFFG = 0.02" in the INCAR file indicates that all atoms are relaxed until the force on each atom is <0.02 eV/Å. The POSCAR file contains the atomic geometry information. The initial lattice parameters in the POSCAR file can be chosen from theoretical³ or experimental references^12,13. The KPOINTS file defines the k poin....

Results

Zigzag BN-NRs encapsulated inside armchair BN-NTs (11,11) were chosen as representative examples for a 1D vdW heterostructure. The lattice parameters were taken from Sahin et al.²⁰. For convenience, zigzag NRs are abbreviated Z_n, where n represents the III–V dimers along the width¹⁴. The encapsulation energy E_L from step 2.3 was used as a rough estimate for the energetic stability of the nanocomposite. The E_L values of Z₂, Z_3.......

Discussion

The calculations for electronic properties in sections 2, 3, and 4 would be similar among various nanoscale materials. The initial atomic model in step 1 should be carefully designed to extract meaningful information. For example, the factor for selecting the model could be the size or chirality of the materials. Also, the initial atomic model in step 1.1 should be reasonably prepared for low-cost structure relaxation. Taking the nanocomposite in the protocol as an example, the NR should be encapsulated inside the NT in .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Nanotube Modeler	Developed by Dr. Steffen Weber	NanotubeModeler1.8	http://www.jcrystal.com/products/wincnt/NanotubeModeler.exe
P4VASP	Orest Dubay	p4vasp 0.3.30	Open source, available at www.p4vasp.at
v2xsf	Developed by Dr. Jens Kunstmann	v2xsf	http://theory.chm.tu-dresden.de/~jk/software.html
VASP software	Computational Materials Physics, Dept. of Physics, University of Vienna	vasp.5.4.1	https://www.vasp.at
VMD software	Theoretical and Computational Biophysics Group, University of Illinois at Urbana-Champaign	vmd1.9.3	https://www.ks.uiuc.edu/Research/vmd
xcrysden	Dept. of Physical and Organic Chemistry, Jozef Stefan Institute	XCrySDen1.5.60	http://www.xcrysden.org/
Xmakemol	Developed by M. P. Hodges	xmakemol5.16	https://www.nongnu.org/xmakemol/XmakemolDownloads.html
Xmgrace software	Grace Development Team under the coordination of Evgeny Stambulchik	xmgrace5.1.25	http://plasma-gate.weizmann.ac.il/Grace/