  Defects influence the properties and functionality of all crystalline
materials. For instance, point defects participate in electronic (e.g. carrier
generation and recombination) and optical (e.g. absorption and emission)
processes critical to solar energy conversion. Solid-state diffusion, mediated
by the transport of charged defects, is used for electrochemical energy
storage. First-principles calculations of defects based on density functional
theory have been widely used to complement, and even validate, experimental
observations. In this `quick-start guide', we discuss the best practice in how
to calculate the formation energy of point defects in crystalline materials and
analysis techniques appropriate to probe changes in structure and properties
relevant across energy technologies.
