electronic surface states of Si(111)-7x7

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leegeunsik · #1 Post by **leegeunsik** » Mon Jul 10, 2006 5:39 am

Dear all,

Have anyone got correct eigenvalues for S2(rest atom induced) surface states?
In the literatures, S2 should be 0.7~0.9 eV below Fermi level.
But my result is 0.5~0.7 eV.
Si(111)-7x7 DAS structure was modeled by 6-layer slab.
Total number of atoms in unit cell is 347 including bottom 49 hydrogens.
I can not understand why VASP gives 0.2 eV higher S2 states.
Could you give any comments?

Regards,
Geunsik

<span class='smallblacktext'>[ Edited ]</span>

#2 Post by **admin** » Tue Jul 11, 2006 8:53 am

have you converged all input parameters as well as the ionic and electronic structure carefully?
by 'literature', do you mean experiments or calculations using different methods

leegeunsik · #3 Post by **leegeunsik** » Mon Jul 17, 2006 5:58 am

I have used default values for EDIFFG, ENCUT.
Also the convergence w.r.t. slab-thickness and energy-cut were checked. Both LDA and GGA potentials were tried.
As to 'literatures', the experimental value is -0.9 eV.
Also PW-calculation by Brommer (Jpan. J. Appl. Phys. 32 pp.1360) gives S2 of -0.7~-0.9 eV.