This is a crystal structure of CsV3Sb5. (a) Room temperature structure with un-distorted kagome nets. (b) and (c) present two in-plane breathing mode candidates, the Star of David (SoD) and the inverse Star of David (ISD) distortions. SoD and ISD are charge density wave ground states.
At low temperatures, the electronic structure of metals becomes unstable, and in some metals, the Fermi surface instability leads to redistributions of the charge density to form a periodic modulation. The modulation of the electron density is called a charge density wave.