INTW: A versatile modular environment for advanced treatment of electronic structure and electron-phonon related properties

We present INTW, a modular software environment designed for advanced electronic structure calculations. Developed in Fortran95, INTW is capable of reading self-consistent field (SCF) results, such as electron energies, wave functions, and potentials, generated by the Quantum ESPRESSO and SIESTA codes. Using these SCF results as input, INTW provides a suite of specialized subroutines and functions for the computation of various electron- and phonon-related physical properties, facilitating detailed analysis of material properties at the quantum level. INTW particularly stands out in its treatment of symmetry, fully exploiting it even when dealing with electron spinor wave functions. Furthermore, it can efficiently work with both localized basis set codes, such as SIESTA, and plane-wave codes like Quantum ESPRESSO. These capabilities make INTW unique, offering a versatile approach that effectively combines the use of symmetry with both localized basis sets and plane-wave methods.