  Orbital-free density functional theory (OF-DFT) is a promising method for
large-scale quantum mechanics simulation as it provides a good balance of
accuracy and computational cost. Its applicability to large-scale simulations
has been aided by progress in constructing kinetic energy functionals and local
pseudopotentials. However, the widespread adoption of OF-DFT requires further
improvement in its efficiency and robustly implemented software. Here we
develop a real-space finite-difference method for the numerical solution of
OF-DFT in periodic systems. Instead of the traditional self-consistent method,
a powerful scheme for energy minimization is introduced to solve the
Euler--Lagrange equation. Our approach engages both the real-space
finite-difference method and a direct energy-minimization scheme for the OF-DFT
calculations. The method is coded into the ATLAS software package and
benchmarked using periodic systems of solid Mg, Al, and Al$_{3}$Mg. The test
results show that our implementation can achieve high accuracy, efficiency, and
numerical stability for large-scale simulations.
