ATLAS (Ab initio orbiTaL-free density functionAl theory Software) is a real-space finite-difference method for solving the orbital-free (OF) DFT Euler–Lagrange equation for periodic systems and its same-name computer software. The method/software is proposed on OF-DFT. Due to its quasilinear scaling behaviour, it can be used to simulate large-scale systems, where contains millions atoms per unit cell.