  As the second component of SPARC (Simulation Package for Ab-initio Real-space
Calculations), we present an accurate and efficient finite-difference
formulation and parallel implementation of Density Functional Theory (DFT) for
extended systems. Specifically, employing a local formulation of the
electrostatics, the Chebyshev polynomial filtered self-consistent field
iteration, and a reformulation of the non-local force component, we develop a
finite-difference framework wherein both the energy and atomic forces can be
efficiently calculated to within desired accuracies in DFT. We demonstrate
using a wide variety of materials systems that SPARC achieves high convergence
rates in energy and forces with respect to spatial discretization to reference
plane-wave result; exponential convergence in energies and forces with respect
to vacuum size for slabs and wires; energies and forces that are consistent and
display negligible `egg-box' effect; accurate properties of crystals, slabs,
and wires; and negligible drift in molecular dynamics simulations. We also
demonstrate that the weak and strong scaling behavior of SPARC is similar to
well-established and optimized plane-wave implementations for systems
consisting up to thousands of electrons, but with a significantly reduced
prefactor. Overall, SPARC represents an attractive alternative to plane-wave
codes for performing DFT simulations of extended systems.
