How can i calculate optical absorption in QE, where the zero phonon line would appear in the absorption curve
Dear friend Khaled A. Abdelghafar
In Quantum Espresso (QE), which is primarily a package for electronic structure calculations, directly calculating the zero-phonon line (ZPL) in the absorption spectrum may not be possible. QE focuses on electronic properties and does not include explicit calculations for phonons or the ZPL.
However, you can still obtain valuable information about the ZPL indirectly by performing calculations related to electron-phonon coupling or using post-processing tools. Here are some approaches and references that can help you gain insights into the ZPL:
1. Electron-phonon coupling: QE can calculate electron-phonon coupling matrix elements using the finite differences method. By computing the electron-phonon coupling, you can obtain information about the broadening and shifts in the absorption spectrum, which indirectly relates to the ZPL. You can refer to the QE documentation, specifically the `dynmat.x` code, for details on performing electron-phonon coupling calculations.
2. post-processing tools: After obtaining the electronic band structure and density of states (DOS) from QE calculations, you can use post-processing tools like Wannier90, BoltzTraP, or other analysis codes to calculate the optical absorption spectrum. These tools can incorporate electron-phonon interactions and provide insights into the ZPL position and intensity. Consult the respective documentation for these post-processing tools to understand their usage and capabilities.
3. External packages: Consider using other software packages that specialize in calculating optical properties, such as density functional perturbation theory (DFPT) or many-body perturbation theory (MBPT) approaches. These packages, like Yambo, ABINIT, or exciting, can include electron-phonon coupling and ZPL calculations within their framework.
When implementing these approaches, it is important to refer to the respective software documentation and research papers to understand the theoretical background, methodology, and practical usage of the tools.
References:
1. Quantum ESPRESSO (QE) documentation: https://www.quantum-espresso.org/resources/docs
2. Wannier90: A. A. Mostofi et al., "wannier90: A tool for obtaining maximally-localised Wannier functions," Comput. Phys. Commun. 178, 685-699 (2008).
3. BoltzTraP: G. K. H. Madsen and D. J. Singh, "BoltzTraP. A code for calculating band-structure dependent quantities," Comput. Phys. Commun. 175, 67-71 (2006).
4. Yambo: A. Marini et al., "Yambo: An ab initio tool for excited state calculations," Comput. Phys. Commun. 180, 1392-1403 (2009).
5. ABINIT: X. Gonze et al., "ABINIT: First-principles approach to material and nanosystem properties," Comput. Phys. Commun. 180, 2582-2615 (2009).
6. C. Friedrich et al., "exciting: A full-potential all-electron package implementing density-functional theory and many-body perturbation theory," J. Phys.: Condens. Matter 29, 383002 (2017).
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