Density-functional theory (DFT) is one of the most reliable simulation methodologies used in materials science. While DFT presents an in-principle exact theory, various approximations are required to perform practical simulations. These approximations can be classified as: (i) controlled approximations, whose errors can be made arbitrarily small at the expense of increased computational cost, and (ii) uncontrolled approximations, whose errors are unknown exactly. In this presentation, we focus on one of the controlled approximations: the k-point mesh density used to integrate the Brillouin zone. We will discuss how it relates to the precision in energy and how the energy precision correlates to the precision of derived quantities. We will also discuss common convergence parameters used in materials databases and what level of precision can be expected as a consequence of such choices.
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