From linear muffin-tin-orbital calculations using suitable basis sets the authors derive, from first principles, sp3 bonding characteristics for group-IV elements. Particular attention is paid to lead, for which the importance of relativistic effects in determining the most stable structure is examined. The mass-velocity shift of the Pb 6s state is so large that the s-p hybridization in a hypothetical diamond structure is too weak to allow the formation of sufficiently strong sp3 bonding. Omission of relativistic effects would make the diamond structure of Pb more stable than the observed (FCC).
 

Physical Review B, 34 5977-80, 1986.