Variation of vacancy formation energy (E 1vF ) with r c of Ashcroft's empty core model potential (AECMP) model for different exchange and correlation functions (ECFs) show almost independent nature but slight variation with ECF for both bcc α iron and fcc γ iron.

The graphs for variation of vacancy formation energy ( ) with rc of Ashcroft's empty core model potential for different exchange and correlation functions are shown for six bcc metals, viz. Li, Na, K, Rb, Cs and Ba. Fitted value of for Li, Na, K, Rb, Cs and Ba are respectively 1.343, 1.694, 2.205, 2.384, 2.962 and 2.337 atomic unit (AU).