  The actinide elemental metals are scare, often toxic and radio active,
causing challenges for both experiments and theory while offering fascinating
physics. For practical purposes they are the prevalent building blocks for
materials where nuclear properties are of interest. Here, however, we are
focusing on fundamental properties of the actinides related to their electronic
structure and characteristic bonding in the condensed state. The series of
actinides is naturally divided into two segments. First, the set of lighter
actinides thorium through plutonium, often referred to as the early actinides,
display variations of their atomic volume reminiscent of transition metals
suggesting a gradual occupation of bonding 5f states. Second, the heavier (or
late) actinides, Am and onwards, demonstrate a volume behavior comparable to
the rare-earth metals thus implying nonbonding 5f states. Arguably, one can
distinguish plutonium metal as special case lying between these two subsets
because it shares some features from both. Therefore, we discuss the early
actinides, plutonium metal, and the late actinides separately applying
first-principles density-functional-theory (DFT) calculations. The analysis
includes successes and failures of the theory to describe primarily phase
stability, bonding, and electronic structure.
