[Pw_forum] PbTiO3 Tetragonal phase optimization problem

[Ari P Seitsonen]

Dear ?? (Name and affiliation?),

   Adding to the first answers, it looks to me that you are using 
Vanderbilt ultra-soft pseudo potentials, but you do not specify a value 
for 'ecutrho'. Did you check that the 'ecutwfc' is sufficient, ie did you 
perform sufficient convergence studies?

     Greetings from Paris,

        apsi

-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-=*=-
   Ari Paavo Seitsonen / Ari.P.Seitsonen at iki.fi / http://www.iki.fi/~apsi/
     Ecole Normale Supérieure (ENS), Département de Chimie, Paris
     Mobile (F) : +33 789 37 24 25    (CH) : +41 79 71 90 935


On Sun, 8 Jan 2017, 朱林光 wrote:

>
>   I am a new qe user,and i have a problem about the PbTiO3 Tetragonal phase optimization using vc-relax, the output result is much less than the accurate one,i dont know how to do such optimization about tetragonal,can you give me some advice,i really appreciate it. this is my input file:
> &control
> calculation = 'vc-relax',
> restart_mode = 'from_scratch',
> pseudo_dir = '$PSEUDO_DIR/'
> outdir = '$OUTPUT_DIR/'
> tstress = .true.
> tprnfor = .true.
> disk_io='high'
> /
> &system
> ibrav=6
> celldm(1)=7.8
> celldm(3)=1.04
> nat=5
> ntyp=3
> ecutwfc=26
> occupations = 'smearing'
> smearing    = "gauss",
> degauss=0.05,
> /
> &electrons
> conv_thr = 1.D-8
> diagonalization   =   'david'
> mixing_beta=0.7D0,
> /
> &IONS
> /
> &CELL
> cell_dynamics='bfgs'
> press=0.00
> /
> ATOMIC_SPECIES
> Pb 207.2  Pb.pz-d-van.UPF
> Ti 47.867  Ti.pz-sp-van_ak.UPF
> O 15.9994  O.pz-van_ak.UPF
> ATOMIC_POSITIONS
> Pb 0.000 0.000 0.000
> Ti 0.500 0.500 0.500
> O 0.000 0.500 0.500
> O 0.500 0.000 0.500
> O 0.500 0.500 0.000
> K_POINTS {automatic}
> 4 4 4 1 1 1
> and output result is :
> Begin final coordinates
>     new unit-cell volume =    401.80625 a.u.^3 (    59.54154 Ang^3 )
> CELL_PARAMETERS (alat=  7.80000000)
>   0.934542602   0.000000000   0.000000000
>   0.000000000   0.934542602   0.000000000
>   0.000000000   0.000000000   0.969470674
> ATOMIC_POSITIONS (alat)
> Pb       0.000000000   0.000000000   0.048659159
> Ti       0.467271301   0.467271301   0.502840681
> O        0.000000000   0.467271301   0.439632316
> O        0.467271301   0.000000000   0.439632316
> O        0.467271301   0.467271301  -0.032489462
> End final coordinates
> the accurate result is 3.9,and c/a is about 1.04, i dont know why my result is smaller than it? please help me,i really appreciate!
>
>
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