  Density functional theory (DFT) codes are commonly treated as a "black box"
in high-throughput screening of materials, with users opting for the default
values of the input parameters. Often, non-experts may not sufficiently
consider the effect of these parameters on prediction quality. In this work, we
attempt to identify a robust set of parameters related to smearing and
tetrahedron methods that return numerically accurate and efficient results for
a wide variety of metallic systems. The effects of smearing and tetrahedron
methods on the total energy, number of self-consistent field cycles, and forces
on atoms are studied in two popular DFT codes: the Vienna Ab initio Simulation
Package (VASP) and Quantum Espresso (QE). From nearly 40,000 computations, it
is apparent that the optimal smearing depends on the system, smearing method,
smearing parameter, and $k$-point density. The benefit of smearing is a minor
reduction in the number of self-consistent field cycles, which is independent
of the smearing method or parameter. A large smearing parameter -- what is
considered large is system dependent -- leads to inaccurate total energies and
forces. Bl\"ochl's tetrahedron method leads to small improvements in total
energies. When treating diverse systems with the same input parameters, we
suggest using as little smearing as possible due to the system dependence of
smearing and the risk of selecting a parameter that gives inaccurate energies
and forces.
