  We present a systematic and comprehensive study of finite-size effects in
diffusion quantum Monte Carlo calculations of metals. Several previously
introduced schemes for correcting finite-size errors are compared for accuracy
and efficiency and practical improvements are introduced. In particular, we
test a simple but efficient method of finite-size correction based on an
accurate combination of twist averaging and density functional theory. Our
diffusion quantum Monte Carlo results for lithium and aluminum, as examples of
metallic systems, demonstrate excellent agreement between all of the approaches
considered.
