[Pw_forum] problem with relaxation of diamond surface

[Khalid Ibne Masood Khalid]

Dear Researchers,
I apologize that this might not be a pwscf problem, but if anyone would
please help me, that would be very helpful.

I am trying to simulate diamond surface. For this I have taken 4 diamond
unit cell on top of each other, and then added a large vacuum space of 30
Angstrom. The crystal that I tried to simulate is shown in the figure
Diamond Single Crystal.png, so that when the crystal will repeat in other
dimensions, it would be a diamond crystal, as shown in figure Diamond
Periodic.png, I believe, the top layer should be diamond (111) surface. Now
whenever I tried to relax this structure, this becomes graphite, I have
simulated it several times, with vdw, without vdw, with PZ pseudopotential,
and with PBE pseudopotential,  all the time it becomes graphite, no diamond
structure persists. I have attached my input file here.

I have also tried a 2*2 supercell of the same crystal, but it becomes
graphite too.

Now my question is am I doing something wrong ? How can I correct this ?  I
would appreciate any help from you.

Thank you,
Khalid Ibne Masood
M,Sc student
Bangladesh University of Engineering and Technology (BUET)
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