Surface Defects and Relative Energies....

Message

danith · #1 Post by **danith** » Mon Dec 17, 2012 9:36 am

Hi VASP' users,

I'm calculating some defects in GaSb surfaces, but my problem is that I'm don't know what happening, because I have my GaSb surfaces, but when replace or Exchange a Sb atom in my GaSb surface by As the AsGaSb surface is most stable. Is it normal in surfaces? what mean?

Thank you in advance for your help...

My INCAR file:

SYSTEM = Ga27 Sb26 As

PREC = Accurate
ENCUT = 500.000
IBRION = 2
NSW = 100
ISIF = 2
ALGO = Normal (blocked Davidson)
NELM = 60
NELMIN = 2
EDIFF = 1.0e-05
EDIFFG = -0.02
VOSKOWN = 1
NBLOCK = 1
ISPIN = 1
INIWAV = 1
ISTART = 0
ICHARG = 2
LWAVE = .FALSE.
LCHARG = .FALSE.
ADDGRID = .FALSE.
ISMEAR = 1
SIGMA = 0.2
LREAL = Auto

POSCAR file:

Ga27 Sb26 As (P1) ~ ConfSearched 1.1 CONTCAR_1 (VASP)
1.0
12.93030000 0.00000000 0.00000000
-6.46515000 11.19796828 0.00000000
0.00000000 0.00000000 20.55750000
27 26 1
Direct
0.22222222 0.11111111 0.59298246
0.00000000 0.00000000 0.77054545
0.11111111 0.22222222 0.41440675
0.22222222 0.44444444 0.59298246
0.00000000 0.33333333 0.77054545
0.11111111 0.55555556 0.41440675
0.22222222 0.77777778 0.59298246
0.00000000 0.66666667 0.77054545
0.11111111 0.88888889 0.41440675
0.55555556 0.11111111 0.59298246
0.33333333 0.00000000 0.77054545
0.44444444 0.22222222 0.41440675
0.55555556 0.44444444 0.59298246
0.33333333 0.33333333 0.77054545
0.44444444 0.55555556 0.41440675
0.55555556 0.77777778 0.59298246
0.33333333 0.66666667 0.77054545

Danith...

alex · #2 Post by **alex** » Mon Dec 17, 2012 11:19 am

Hi Danith, by what means do you conclude?

Cheers,

alex

danith · #3 Post by **danith** » Mon Dec 17, 2012 3:16 pm

Hi Alex, I don't know Alex and I don't sure because is my first time doing surfaces using vasp, but I thinking that It is wrong because the As atoms are impurities... Just I want to know other opinions... What do you think?

alex · #4 Post by **alex** » Mon Dec 17, 2012 4:01 pm

Did you just compare the 2 total energies?

danith · #5 Post by **danith** » Mon Dec 17, 2012 4:11 pm

Yes!!! of course, Ga(27)Sb(27) surface (-196.8803 eV) and Ga(27)Sb(26)As(1)=-203.4756 eV... In this case the GaSbAs surface is most stable or not?
<span class='smallblacktext'>[ Edited Mon Dec 17 2012, 04:26PM ]</span>

alex · #6 Post by **alex** » Mon Dec 17, 2012 4:31 pm

ok, it's not that easy.
You need to do more thermodynamics, e.g. with 'reservoirs' of As and Sb.

There is a nice overview: http://www.tcm.phy.cam.ac.uk/~mdt26/tti ... taa_08.pdf
check slide 33 for the basic idea.

About the 'howto' there is a lot(!) of literature around. Just dig a little and figure out what suites you most.

Cheers,

alex