EPW-VASP interface for first-principles calculations of electron-phonon interactions

TL;DR

The paper presents the EPW-VASP interface, enabling first-principles electron–phonon calculations by transferring real-space data from VASP to EPW for Wannier–Fourier interpolation on dense grids. It integrates PAW-based finite-displacement EPI data with EPW’s interpolation and long-range polar corrections, and demonstrates accuracy by reproducing MgB$_2$ superconducting properties and cubic BN transport across exchange–correlation functionals. The results show good agreement with QE-based workflows while enabling access to VASP-available functionals (e.g., r$^2$SCAN) and PAW pseudopotentials. This interface broadens the interoperability of EPI calculations, supporting more versatile materials design and high-throughput studies, with future plans including 2D extensions, quadrupole corrections, and polaron analyses.

Abstract

We present an interface between the Vienna \textit{Ab initio} Simulation Package (VASP) and the EPW software for calculating materials properties governed by electron-phonon (e-ph) interactions. Computation of the e-ph matrix elements with the finite-difference supercell approach in VASP and their fine-grid interpolation in EPW enable accurate modeling of temperature-dependent materials properties and phonon-assisted quantum processes with VASP's extensive library of exchange-correlation functionals and pseudopotentials. We demonstrate the functionality of the EPW-VASP interface by examining the superconducting gap and critical temperature in MgB$_2$ using the anisotropic Migdal-Eliashberg equations, and the carrier mobility in cubic BN using the \textit{ab initio} Boltzmann transport equation.

Figures (6)

• Figure 1: General workflow for transformations from Wannier to Bloch space in the EPW-VASP interface. Solid arrows indicate the default route; the alternative route along the dotted arrows is followed when long-range effects are included. Quantities in the Wannier gauge are marked with a superscript "W". The symbols $\mathcal{L}$ and $\mathcal{S}$ denote long- and short-range contributions, respectively. Abbreviations: "FT" - standard Fourier transformation between commensurate $({{\bf R}_p}, {{\bf R}_{p^\prime}})$ and coarse $({\bf k}, {\bf q})$ grids; "FI" - Fourier interpolation from $({{\bf R}_p}, {{\bf R}_{p^\prime}})$ to fine $({{\bf k}^\prime}, {{\bf q}^\prime})$ grids; "WR" - Wannier rotation from the Wannier to the Bloch gauge via the unitary matrices $\mathcal{U}_{{{\bf k}^\prime}}$, $\mathcal{U}_{{{\bf k}^\prime} + {{\bf q}^\prime}}$ defined in Eqs. \ref{['eq:EPWHamBloch']} and \ref{['eq:ElphBloch']}; "D" - diagonalization of the dynamical matrix. For the electron-phonon matrix, two sequential Fourier transformations are first carried out to obtain matrix elements on a differently ordered $({{\bf R}_p}, {{\bf R}_{p^\prime}})$ grid [as opposed to $({{\bf R}_p}, {{\bf R}_{p^{\prime\prime}}})$], required by the difference in conventions between VASP and EPW discussed in Section \ref{['sec:conventions']}.
• Figure 2: Flowchart illustrating the required input files and data transfer between VASP and EPW using the EPW-VASP interface. On the left side, the electron-phonon matrix elements, Hamiltonian, and IFCs computed in VASP with the finite displacement approach in real space are rewritten to an HDF5 file in the Wannier representation. On the right side, EPW reads the HDF5 file and interpolates the quantities onto a fine Bloch grid for subsequent superconductivity and transport calculations.
• Figure 3: MgB$_2$ properties calculated using QE-PBE (black), VASP-PBE (red), and VASP-r$^2$SCAN (green). The top panels show (a) band structure, (b) phonon dispersion, (c) phonon density of states, and (d) Eliashberg spectral function $\alpha^2F$ with integrated electron-phonon coupling strength $\lambda$. The bottom panels display energy distributions of the superconducting gap $\Delta_{{\bf k}}$ as a function of temperature, with insets illustrating histograms of the electron-phonon coupling strength $\lambda_{{\bf k}}$. In (b), the blue stars are inelastic X-ray scattering experimental data at 300 K from Ref. Shukla2003.
• Figure 4: Cubic BN properties calculated using QE-PBE (black), VASP-PBE (red), and VASP-r$^2$SCAN (green). The panels show (a) band structure, (b) phonon dispersion, and (c) hole drift mobility calculated with aiBTE including long-range dipole corrections. In (c), the blue star marks the 300 K result from Ref. Ponce2021.
• Figure 5: Wigner-Seitz construction for centers ${\bf r}_m$, ${\bf r}_n$, and unit cell ${\bf R}_{1, 1}$ in the $2\times2$ BvK supercell. Infinite periodic grid is outlined by dashed gray lines. Points ${\bf r}_m$ (green star) and ${\bf r}_n$ (marked gray ring) are placed inside the unit cell ${\bf R}_{0, 0}$ (light gray shade). Point ${\bf r}_n + {\bf R}_{1,1}$ (solid red circle) is inside the top right unit cell ${\bf R}_{1, 1}$ (black dashed lines) of the $2~\times~2$ BvK supercell (black solid lines). Among ${\bf r}_n + {\bf R}_{1,1}$ and its replicas (red rings), only the replica falling inside the WS supercell centered around ${\bf r}_m$ (solid green lines) has minimal distance to ${\bf r}_m$ (see the red arrow). Selected ${\bf R}_p = {\bf R}_{1,1} + {\bf T}_{-1, 0}$ corresponds to the vector of the unit cell this replica is located in.