  First-principles density functional theory (DFT) with plane wave (PW) basis
set is the most widely used method in quantum mechanical material simulations
due to its advantages in accuracy and universality. However, a perceived
drawback of PW-based DFT calculations is their substantial computational cost
and memory usage, which currently limits their ability to simulate large-scale
complex systems containing thousands of atoms. This situation is exacerbated in
the new Sunway supercomputer, where each process is limited to a mere 16 GB of
memory. Herein, we present a novel parallel implementation of plane wave
density functional theory on the new Sunway supercomputer (PWDFT-SW). PWDFT-SW
fully extracts the benefits of Sunway supercomputer by extensively refactoring
and calibrating our algorithms to align with the system characteristics of the
Sunway system. Through extensive numerical experiments, we demonstrate that our
methods can substantially decrease both computational costs and memory usage.
Our optimizations translate to a speedup of 64.8x for a physical system
containing 4,096 silicon atoms, enabling us to push the limit of PW-based DFT
calculations to large-scale systems containing 16,384 carbon atoms.
