[Pw_forum] scf convergence calculation

[Francesca Costanzo]

Dear PWSCF users,

I am doing a scf calculation on si(100) slab surface.
I have tested two pseudo potentials fo silicon to see
which performs better.

I am wondering why  using
the   Si.pbe-n-van.UPF and Si.pw91-n-van.UPF pseudoes
in the first case I can reach quite easily ( after 400 
iterations) the convergence while in the latter case after 1200 iterations 
I still don't reach the convergence.
the mixing beta is 0.5.

Is there something wrong?

Anyway the input file is below:

   # self-consistent calculation
     cat > si-ex01.in << EOF
&control
     calculation='scf'
     prefix='si',
     tstress = .true.
     tprnfor = .true.
     restart_mode='restart',
     pseudo_dir ='/sfs/sanfs/home/userincm/incbo407/PWscf/pseudo/',
     outdir='/scratch/incbo407/au-PWscf/tmp-1/',
     etot_conv_thr = 1.d-4
   /
  &system
     ibrav = 8, celldm(1) = 29.02243, celldm(2) =1.0, celldm(3)= 0.89771, 
nat=56, ntyp=2,  ecutwfc=18.0,
  /
  &electrons
     mixing_mode = 'plain'
     mixing_beta = 0.5
     conv_thr =  1.0d-8
  /
  &ions
  /
ATOMIC_SPECIES
Si 28.086 Si.pw91-n-van.UPF
H   1     H.pw91-van_ak.UPF
ATOMIC_POSITIONS {angstrom}
  Si -.486986953827 -.486915661371 .021837699340
  Si 3.254734080912 3.254554580350 -.715466406181
  Si .424995921464 5.989287334956 -.032510900988
  Si 1.908574447668 7.596205581111 -.896329755432
  Si 5.990175519344 .425574367605 -.031655667742
  Si 7.597289525085 1.909448358802 -.895741285772
  Si 4.863694686691 4.863621862511 -.928089502092
  Si 9.019734606435 9.020000340300 -.836996926760
  Si 1.332006439043 4.282396930595 -1.483511378893
  Si 4.282762677873 1.331640602610 -1.482720710139
  Si 1.215421638705 9.726643706866 -1.436019240017
  Si 4.069065518611 6.940868463489 -1.558148325068
  Si 6.941730748367 4.070143770542 -1.556740812199
  Si 9.727400143869 1.215885487447 -1.436139812232
  Si 6.926671693616 9.825186228268 -1.480679150046
  Si 9.825040961721 6.927019069098 -1.481122837636
  Si 2.752199364097 -.023268345504 -2.733402882614
  Si -.022185141426 2.752036538539 -2.734578963613
  Si 2.755879272416 5.496899501655 -2.970326566691
  Si -.004779806850 8.317568614429 -2.969974442472
  Si 8.317316174588 -.004017804657 -2.969192076227
  Si 5.498360672151 2.755878723458 -2.968474960855
  Si 8.346177303503 5.558752009571 -2.782863187750
  Si 5.557877655641 8.346312021303 -2.782400281184
  Si 1.389966664098 1.388183764950 -4.139518840077
  Si 1.366337053897 6.940229376004 -4.258916306178
  Si 4.151574127028 4.149476803004 -4.278767316434
  Si 4.138929512730 9.694066210006 -4.160002340210
  Si 6.940071554385 1.366577579401 -4.258586275398
  Si 9.693861222560 4.139131304691 -4.160296524367
  Si 6.925553051516 6.926722417990 -4.154730726999
  Si 9.700291030289 9.701542440060 -4.273212145658
  Si .000000000000 .000000000000 -5.538591342479
  Si 2.769296729594 2.769296729594 -5.538591342479
  Si .000000000000 5.538591342479 -5.538591342479
  Si 2.769296729594 8.307892305490 -5.538591342479
  Si 5.538591342479 .000000000000 -5.538591342479
  Si 8.307892305490 2.769296729594 -5.538591342479
  Si 5.538591342479 5.538591342479 -5.538591342479
  Si 8.307892305490 8.307892305490 -5.538591342479
  H .847478422628 -.846884685755 -6.504440365581
  H -.847316494390 .847694326946 -6.503794769337
  H 3.610082118376 1.928241460414 -6.515886469477
  H 1.917014435899 3.621363118971 -6.495428477030
  H .852174341536 4.685717428620 -6.494724671289
  H -.840461532306 6.379649786722 -6.516156349874
  H 3.616235391428 7.460033933598 -6.504011732009
  H 1.921872283045 9.155369669764 -6.503953522512
  H 6.383803828126 -.844617690420 -6.508975414605
  H 4.685555500382 .852282293694 -6.494454790892
  H 9.156068183733 1.921926259125 -6.503307926268
  H 7.460679529841 3.616289367507 -6.504710245978
  H 6.385587155455 4.690845156163 -6.504170485184
  H 4.690683227924 6.386073998525 -6.503524888940
  H 9.160391561857 7.455445966849 -6.494835798512
  H 7.462679819843 9.153210626588 -6.508329818361
K_POINTS {automatic}
4   4   1  0  0  0
EOF


thank you.
 		Francesca Costanzo
-- 
Francesca Costanzo, Ph.D.
Dipartimento di Chimica Fisica ed Inorganica
Viale Risorgimento 4
40136 Bologna
tel.0039-051-2093710
fax 0039-051-2093690