WannierBSE: High-Performance Bethe-Salpeter Equation Solver

Getting Started | Technical Workflow | Examples | Citation | Credits | Supported By

WannierBSE is a high-performance computational suite for solving the Bethe–Salpeter Equation (BSE) within a Wannier tight-binding framework. Specifically optimized for two-dimensional materials, it combines first-principles electronic-structure accuracy with the efficiency of Wannier-based interpolation.

The general workflow begins with a density functional theory (DFT) calculation performed using Quantum ESPRESSO, VASP, or another first-principles code compatible with Wannier90. The DFT results are then processed with Wannier90 to construct a localized Wannier representation of the electronic structure. WannierBSE uses the generated Wannier Hamiltonian and related matrix elements to construct and solve the BSE.

By leveraging MATLAB’s numerical capabilities, WannierBSE enables researchers to calculate exciton energies, excitonic wavefunctions, optical spectra, transition dipoles, and light–matter interactions in complex dielectric environments.

To get started with WannierBSE, please refer to our comprehensive documentation:

• User Guide (PDF) - Detailed technical manual and theory.
• QuickStart Guide (PDF) - Brief setup and first run instructions.
• Official Website - News and updates.

• MATLAB (Recommended: R2020b or later)
• Parallel Computing Toolbox (Highly recommended for large-scale calculations)

WannierBSE features a modular data pipeline designed to handle both raw generation and pre-computed data ingestion.

WannierBSE supports direct-interaction calculations and, in v1.1, calculations including short-range electron-hole exchange.

🔄 Direct-Interaction Route: Users may either place wannier90_hr.dat in /User_input/ and let WannierBSE generate the k-mesh and tight-binding bands internally, or provide a matched external dataset using kmesh.txt and TB_data/ files such as v*_TB.txt and c*_TB.txt. Structural information is read from structure.txt or wannier90.win in /User_input/.

📥 Direct + Short-Range Exchange Route: Exchange-enabled calculations require the internal Wannier90-based workflow. In addition to wannier90_hr.dat, users must provide real-space spinor Wannier functions in /User_input/Wannier_functions_xsf/, unless the required processed Wannier-function and exchange-interaction caches already exist in /Precomputed_data/.

Dielectric Input: For both routes, users may provide epsilon.txt in /User_input/; otherwise WannierBSE generates or loads dielectric data from /Precomputed_data/.

The simulation environment is governed by dedicated control files located in the /Parameters/ directory:

• control.txt, WTB_control.txt, WF_centers.txt
• kmesh_control.txt, dielectric_control.txt
• exchange_control.txt

1. Core Solver: Execute WBSE.m in MATLAB. The script utilizes an optimized, symmetry-aware Hamiltonian constructor and a high-performance parallelized solver.
2. Post-Processing: Use the auxiliary script Ex_plot.m to visualize the exciton energy spectrum.
3. Data Management: Main outputs, including energy spectra (Ex.mat) and wavefunctions (A.mat), are saved in the /Exciton_data/ folder together with run-related output files.

To help you get started quickly, we provide several pre-configured examples in the repository. These include sample input files and parameters for direct-interaction and direct-plus-short-range-exchange workflows in typical 2D materials.

📂 Browse Examples in the Repository

Each example includes:

• User input and precomputed data files
• Ready-to-use control parameter files
• Expected results.

Examples 05, 06, and 07 use Wannier90 spinor projection files to reproduce the reported results. These files are not included in WannierBSE_v1.1.zip because of their size.

To reproduce these examples, download WannierBSE_v1.1_Wannier90_spinor_projections.zip from the v1.1 GitHub Release and extract the Wannier_functions_xsf folder into the corresponding User_input/ folder. The large precomputed WF_up.mat and WF_down.mat cache files for these examples are also provided as separate v1.1 release assets.

To support the continued development of WannierBSE, please cite the following references:

Primary Reference: Peng, G.-H. et al. "Distinctive Signatures of the Spin- and Momentum-Forbidden Dark Exciton States in the Photoluminescence of Strained WSe2 Monolayers under Thermalization", Nano Lett. 19, 4, 2299–2312 (2019). https://doi.org/10.1021/acs.nanolett.8b04786

Non-local Dielectric Function: Li, W.-H. et al. "The Key Role of Non-Local Screening in the Environment-Insensitive Exciton Fine Structures of Transition-Metal Dichalcogenide Monolayers", Nanomaterials 13, 11, 1739 (2023). https://doi.org/10.3390/nano13111739

Developed by the research group of Prof. Shun-Jen Cheng at National Yang Ming Chiao Tung University (NYCU).

Core Developers:

• Dr. Ping-Yuan Lo, Dr. Wei-Hua Li, Dr. Guan-Hao Peng, Dr. Jhen-Dong Lin, Dr. Vo Khuong Dien, Dr. Oscar Javier Gomez Sanchez, Mr. Ching-Hung Shih, Mr. Kun-Yi Lin, and Prof. Shun-Jen Cheng.

We gratefully acknowledge the support from the following organizations: