Sorry Marcos, error cancellation is important here, because absolute energy convergence may never be assured, least for big boxes. Thus one should use Et(1)=Et(64)/64 or, equivalently, scale the result for the perfect lattice box of 64 Fe atoms to 63.
Regards, Roberto On Fri, 1 Aug 2008, Marcos Verissimo Alves wrote: > Hi Roberto, > > This seems to be ok. Just one thing: make sure Et(1) is the total energy > of the isolated atom (that is, place it in a box big enough that you have > it isolated). Also, since you can write down the unit cell of bcc-Fe with > a single atom, you can simply take the energy of the unit cell, multiply > it by 64 and save yourself the computation time for calculating Et(64). > > Marcos >
