[Pw_forum] A problem about relax

[Nicola Marzari]

Dear Lihui,

1) You are using a Vanderbilt ultrasoft pseudopotential -
a proper cutoff is more likely in the range of 25 to 30 Ry, not 70.

2) ecutrho is by default 4 times ecutwfc (you need a cutoff
radius 2 as large for the charge density than for the wfc,
if the charge density if the square of wfc). The ultrasoft
formulation makes the wfc smoother than that, but there is nothing that 
can be done for the charge density - whose natural cutoff is
dictated by physics. In practice, use ecutrho 8 times ecutwfc.
Ecutrho = 0 does not make sense.

3) use smaller beta than 0.7 for these systems.

Of course, before doing this, you (and everyone else reading
this list) should have tested extensively a 1-atom fcc bulk Pt
system, to make sure everything worked properly.

I strongly advice some reading (e.g. Richard Martin excellent book) -
or carefully study the material at
http://www.quantum-espresso.org/wiki/index.php/Tutorials_and_Examples


		nicola

oulihui666 wrote:
> Dear pwscf users:
>       I am now doing a large job of 'relax' calculation. The unit cell 
> contains 20 atoms and vacuum. The job has been running for seven days. 
> While the total energy is decreasing, the amount it decreases is 
> approximately a constant. We calculated the Pt(111) surface with pwscf, 
> we use a five-layer slab containing 20 Pt atoms,  the atoms in the 
> bottom three layers are fixed, and the others are allowed to relax. The 
> input file and structure can be found in below. However, calculated 
> results indicated, the atoms in the top two layers are not inward or 
> outward relaxation, but upward or downward relaxation,  Could you tell 
> me whether the input file is correct or not? and the final structure is 
> correct or not please?
> Thanks a lot
> Best wishes
> Lihui Ou
> 
>  
> 
> &CONTROL
> 
>                  calculation = 'relax' ,
> 
>                 restart_mode = 'from_scratch' ,
> 
>                       outdir = '/home/olh/tmp/' ,
> 
>                   pseudo_dir = '/home/olh/pseudo/' ,
> 
>                       prefix = 'Pt111_20' ,
> 
>                      tstress = .true. ,
> 
>                      tprnfor = .true. ,
> 
>  /
> 
>  &SYSTEM
> 
>                        ibrav = 4,
> 
>                            A = 5.549 ,
> 
>                            B = 5.549 ,
> 
>                            C = 21.062 ,
> 
>                        cosAB = -0.5 ,
> 
>                        cosAC = 0 ,
> 
>                        cosBC = 0 ,
> 
>                          nat = 20,
> 
>                         ntyp = 1,
> 
>                      ecutwfc = 70 ,
> 
>                      ecutrho = 0 ,
> 
>                  occupations = 'smearing' ,
> 
>                      degauss = 0.02 ,
> 
>                     smearing = 'gaussian' ,
> 
>  /
> 
>  &ELECTRONS
> 
>                     conv_thr = 1.0D-8 ,
> 
>                  mixing_beta = 0.7D0 ,
> 
>              diagonalization = 'david' ,
> 
>  /
> 
>  &IONS
> 
>  /
> 
> ATOMIC_SPECIES
> 
>    Pt  195.09000  Pt.pz-rrkjus.linux.UPF
> 
> ATOMIC_POSITIONS angstrom
> 
>    Pt     -0.000000000    0.000000000   -9.062000000    0  0  0
> 
>    Pt     -0.000000000    2.775000000   -9.062000000    0  0  0
> 
>    Pt      2.403000000   -1.387000000   -9.062000000    0  0  0
> 
>    Pt      2.403000000    1.387000000   -9.062000000    0  0  0
> 
>    Pt     -0.000000000   -0.000000000   -2.265000000    1  1  1
> 
>    Pt     -0.000000000    2.775000000   -2.265000000    1  1  1
> 
>    Pt      2.403000000   -1.387000000   -2.265000000    1  1  1
> 
>    Pt      2.403000000    1.387000000   -2.265000000    1  1  1
> 
>    Pt      1.602000000    0.000000000   -4.531000000    0  0  0
> 
>    Pt      1.602000000    2.775000000   -4.531000000    0  0  0
> 
>    Pt      4.005000000   -1.387000000   -4.531000000    0  0  0
> 
>    Pt      4.005000000    1.387000000   -4.531000000    0  0  0
> 
>    Pt      0.801000000    1.387000000   -6.796000000    0  0  0
> 
>    Pt      0.801000000    4.162000000   -6.796000000    0  0  0
> 
>    Pt      3.204000000    0.000000000   -6.796000000    0  0  0
> 
>    Pt      3.204000000    2.775000000   -6.796000000    0  0  0
> 
>    Pt      0.801000000    1.387000000   -0.000000000    1  1  1
> 
>    Pt      0.801000000    4.162000000   -0.000000000    1  1  1
> 
>    Pt      3.204000000   -0.000000000   -0.000000000    1  1  1
> 
>    Pt      3.204000000    2.775000000   -0.000000000    1  1  1
> 
> K_POINTS automatic
> 
>   3 3 1   1 1 1
> 
>  
> 
> --
> ======================================
> Lihui Ou
> PH.D Candidate in Electrochemistry                     
> College of Chemistry and Molecular Science           
> Wuhan University,/430072/,Hubei Province,China 
> /E-mail:oulihui666 at 126.com <mailto:oulihui666 at 126.com>/
> ======================================

-- 
---------------------------------------------------------------------
Prof Nicola Marzari   Department of Materials Science and Engineering
13-5066   MIT   77 Massachusetts Avenue   Cambridge MA 02139-4307 USA
tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu