Dear Feng, As Heiko indicates, your in-plane parameters are too large; more than 16 Angstrom. your lattice parameters, as Heiko says, are *multiplied* by the lattice constant, a choice like
1.0 1.0 4.0 90 90 90 may be more sensible one, that will allow for atomic bonding on the x-y plane. I don't know if my actual choice makes sense, the point to understand is that your first two lattice parameters are too large as you defined them, and you must reduced them accordingly if in need to study a slab. Best regards, -Salvador. ----- Original Message ----- From: "Fen Hong" <gm030...@gmail.com> To: siesta-l@uam.es Sent: Friday, January 15, 2010 2:17:07 AM GMT -05:00 US/Canada Eastern Subject: Re: [SIESTA-L] the surface was totally changed after calculation Heiko-san, thank you very much. I cannot understand that " choose some larger value for the axis perpendicular to the surface to simulate a surface layer" so I have to add vacuum layer to this system? Thank you very much Fen Hong
