QERaman: An open-source program for calculating resonance Raman spectra based on Quantum ESPRESSO

TL;DR

QERaman closes a gap in first-principles Raman spectroscopy by enabling first-order resonance Raman calculations from Quantum ESPRESSO outputs through complex Raman tensors. It combines electron-photon and electron-phonon matrix elements, computed with modified QE codes, to yield resonance intensities $I(E_L,E_{RS})$ and polarization-resolved spectra, including circularly polarized-light (CPL) helicity effects. The paper provides installation guidance, a four-step workflow, and hands-on tutorials for graphene and MoS$_2$, highlighting convergence considerations and the impact of lifetimes and excitonic effects. This open-source tool lowers barriers for experimentalists to interpret resonance Raman data and enables direct theory–experiment comparisons, with future extensions toward double-resonance regimes.

Abstract

We present an open-source program QERaman that computes first-order resonance Raman spectroscopy of materials using the output data from Quantum ESPRESSO. Complex values of Raman tensors are calculated based on the quantum description of the Raman scattering from calculations of electron-photon and electron-phonon matrix elements, which are obtained by using the modified Quantum ESPRESSO. Our program also calculates the resonant Raman spectra as a function of incident laser energy for linearly- or circularly-polarized light. Hands-on tutorials for graphene and MoS$_2$ are given to show how to run QERaman. All codes, examples, and scripts are available on the GitHub repository.

Figures (6)

• Figure 1: Raman scattering process, in which $E_L$ is laser energy of optical light source, and $\hbar\omega_\nu$ is the phonon frequency at $\nu$ mode.
• Figure 2: Flowchart of the process to calculate the first-order resonance Raman spectra. Four steps are required for the calculation of the resonance Raman spectra. In the first step, the band structure and the wavefunctions of the material are computed by the self-consistent field (SCF) calculation with pw.x of QE. In the second step, the dipole vector (see Eq. \ref{['eq:elpt15']}) is calculated by bands_mat.x of QERaman. In the third step, the electron-phonon matrix elements (see Eq. \ref{['eq:elph1']}) is calculated by ph_mat.x of QERaman. Finally, the complex Raman tensor (see Eq. \ref{['eq:5']}) and the Raman spectra (see Eq. \ref{['eq:4']}) are calculated by raman.x of QERaman. The top and bottom figures are the logo of QE and QERaman, respectively.
• Figure 3: Helicity-dependent Raman spectra of graphene at the laser energy of 2.33 eV for several k-points grids.
• Figure 4: Polarized Raman intensities for linearly-polarized light are plotted for the doubly-degenerate $E_{2g(1)}$ (a) and $E_{2g(2)}$ (b) based on the complex Raman tensors.
• Figure 5: Helicity-dependent Raman spectra of monolayer MoS$_2$ at 1.95, 2.33, 2.54, and 2.87 laser energies.