QR2-code: An open-source program for double resonance Raman spectra

We present an open-source program QR2-code that computes double-resonance Raman (DRR) spectra using first-principles calculations. QR2-code can calculate not only two-phonon DRR spectra but also single-resonance Raman spectra and defect-induced DRR spectra. For defect-induced DRR 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 QR2-code for single-resonance, double-resonance, and defect-induced Raman spectra. We also compare the single-resonance Raman spectra by QR2-code with that by QERaman code. In QR2-code, the Raman spectrum is calculated by the time-dependent perturbation theory, in which the energy dispersions of electron and phonon are taken from Quantum ESPRESSO (QE) code and the electron-phonon matrix element is obtained from the modified Electron-Phonon-Wannier (EPW) code. All codes, examples, and scripts are available on the GitHub repository.