Tipping the Balance Between the bcc and fcc Phase Within the Alkali and Coinage Metal Groups

Why the Group 1 elements crystallize in the body-centered cubic (bcc) structure, and the iso-electronic Group 11 elements in the face-centered cubic (fcc) structure, remains a mystery. Here we show that a delicate interplay between many-body effects, vibrational contributions and dispersion interactions obtained from relativistic density functional theory offers an answer to this long-standing controversy. It also sheds light on the Periodic Table of Crystal Structures. A smooth diffusionless transition through cuboidal lattices gives a detailed insight into the bcc -> fcc phase transition for the Groups 1 and 11 elements. Relativistic density functional calculations for the cuboidal phase transition show that small effects such as dispersion interactions and phonon contributions can tip the balance between the body-centered and face-centered cubic structures shedding light into the difference between the Groups 1 and 11 elements in the Periodic Table.image