[Pw_forum] wurtzite AlN

[Helen]

Hi,
I've successfully calculated the bandstructure for zinc-blende AlN, and I wanted to do the same for wurtzite AlN but am running into problems. I started off with a=5.88 a.u. c/a=1.600 and u=0.382 , I then kept a and c constant and altered u. The results showed that u needed to be smaller but when I reached u=0.369 my scf calculations stopped converging. I tried using both cg and davidson diagonalization. I then tried keeping u constant and altering c, I don't get convergence problems but I get unrealistically small values of c. Also the bandgap data I'm getting is nonsense (no band gap at all). Perhaps I have a mistake in my input file?
Thank you for your help and advice,
Dr. Helen Eisenberg (Fritz Haber Center, Hebrew University)

 &control
    calculation='scf'
    restart_mode='from_scratch',
    tstress = .true.
    tprnfor = .true.
    prefix='alas',
    pseudo_dir = '$PSEUDO_DIR/',
    outdir='$TMP_DIR/'
 /
 &system    
    ibrav=  4, celldm(1) =5.88, celldm(3)=1.600, nat=  2, ntyp= 2,
    ecutwfc =80.0, nbnd = 8,
    nr1=32,
    nr2=32,
    nr3=32,
    ecutrho = 240.0
 /
 &electrons
    conv_thr =  1.0d-6
    mixing_beta = 0.7
 /
ATOMIC_SPECIES
 Al  26.98  Al.vbc.UPF
 N   14.007  N.pz-vbc.UPF
ATOMIC_POSITIONS
 Al 0.00 0.00 0.00 
 N 0.00 0.00 0.611
K_POINTS (automatic)
4 4 4 0 0 0
EOF
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