Hi, > This may seem silly, but I'm confused as to what > exactly the number of > atoms in a unit cell is (nat). For example, the > Silicon example says > that nat is only two, yet a diamond structure such > as this should have > much more than two atoms per unit cell.
Let us consider the diamond case. If you choose as basis vectors next 3 vectors (which are the standard choice) 1/2, 1/2, 0 1/2, 0 , 1/2 0 , 1/2, 1/2 you have only 2 atoms in the unit cell (parallelepiped) spanned by these vectors: 0, 0, 0 1/4, 1/4, 1/4 If you decide to choose as basis vectors next 3 ones 1 0 0 0 1 0 0 0 1 you have 8 atoms in the unit cell which is now a cub. If your choice is the latter for CaF2 structure you will have 12 atoms, but using the former - only 3. So, number of atoms (nat) in a unit cell depends on your unit cell choice defined by 3 basis vectors. > Is the definition of nat the number of basis > vectors? To me it is not so clear, but see above. Bests, Eyvaz. > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
