The properties of condensed matter at ultrahigh pressures are of considerable current
interest not only in solid state physics, but also in geophysics and in material science.
From a fundamental point of view, the behaviour of matter under extreme pressure
conditions shed light on the properties of bonding through the study of the modification
of the electronic structure induced by the decrease of the interatomic distances. These
modifications can lead the system to new ground states with different physical and chemical
properties, thus providing the driving mechanism of structural phase transitions.
