QR$^2$-code: An open-source program for double resonance Raman spectra

TL;DR

QR$^2$-code is an open-source software that calculates various types of Raman spectra, including double-resonance, single-resonance, and defect-induced spectra, using first-principles methods and integrating multiple computational tools.

Contribution

It introduces a comprehensive open-source tool that combines first-principles calculations for diverse Raman spectra, facilitating easier and more accurate spectral analysis.

Findings

Successfully computes double-resonance Raman spectra from first-principles.

Provides validation by comparing with existing QERaman code.

Includes tutorials demonstrating practical usage for graphene.

Abstract

We present an open-source program, QR$^2$-code, that computes double-resonance Raman (DRR) spectra using first-principles calculations. QR$^2$-code can calculate not only two-phonon DRR spectra but also single-resonance Raman spectra and defect-induced DRR spectra. For defect-induced DDR spectra, we simply assume that the electron-defect matrix element of elastic scattering is a constant. Hands-on tutorials for graphene are given to show how to run QR$^2$-code for single-resonance, double-resonance, and defect-induced Raman spectra. We also compare the single-resonance Raman spectra by QR$^2$-code with that by QERaman code. In QR$^2$-code, the energy dispersions of electron and phonon are taken from Quantum ESPRESSO (QE) code, and the electron-phonon matrix element is obtained from the electron-phonon Wannier (EPW) code. All codes, examples, and scripts are available on the GitHub repository.