Behavior of Hydrogen and Hydrides Under Pressure

Hydrogen, the simplest and most abundant element of the universe, has proven to be an enigma for high pressure physics. Its predicted metallization and superconductivity under pressure has motivated numerous experimental and theoretical developments in the field of high pressure physics. This chapter summarizes the present understanding of hydrogen under compression. In many cases, hydrides are perceived to represent a chemically pre-compressed state of hydrogen, giving impetus to their investigations, including search for high pressure superconductivity. Due to its current and intense interest, this topic is covered separately in this chapter.