[Pw_forum] Why there difference between my results and those reported.

[Eyvaz Isaev]

Hi,

>however what I got by pwscf is not the same with
those >reported in, for
>example, PRB86,4656, which follows the LAPW method.

I did even phonons for MgB2 and found it in good
agreement with experiments.

>Thus I want to
> know why there are differences and how can I get a
> reliable electronic
> structure which may be used to analyse to get
> properties of materials?

May be you used k-points wrt lattice vectors, but they
should be in cartesian.

>And  further more why I can't use pseudopotentials in
> format of .fhi, and will 
> there be any differece in the results with different
> PPs?

You can use FHI PsP, but it should be converted to the
UPF format. Please see /upftools directory.

By the way, my apologies for my suggestion that one
can convert TM PsP from ABINIT to the UPF format.
Sorry, it is not correct. ncpp2upf can convert NC PsP
generated  by Paolo's atomic (ld1) code.

Sure, using different PsPs you will get slighltly
different (physical) results (i.e. lattice parameter,
bulk modulus, band energies wrt the Fermi level,
phonon modes, etc.). Though, total energies and bands
themselves  will be different.
   
Nothing seems to be wrong in your input file.
So, analyse your output files  and k-points for band
structure calculations.

Bests,
Eyvaz.

>   Thank you in advance.
> Here is my input file for MgB2:
>  &CONTROL
>                  calculation = 'scf' ,
>                 restart_mode = 'from_scratch' ,
>                       outdir = '/pwscf/tmp/' ,
>                   pseudo_dir = '/pwscf/pseudo/' ,
>                       prefix = 'mgb' ,
>                      tstress = .true. ,
>                      tprnfor = .true. ,
>                      tefield = .false. ,
>  /
>  &SYSTEM
>                        ibrav = 4,
>                    celldm(1) = 5.829996,
>                    celldm(3) = 1.14100,
>                          nat = 3,
>                         ntyp = 2,
>                      ecutwfc = 30.0 ,
>                         nbnd = 8,
>                  occupations = 'tetrahedra' ,
>  /
>  &ELECTRONS
>                     conv_thr = 1.0d-8 ,
>                  mixing_beta = 0.7 ,
>              diagonalization = 'cg' ,
>  /
> ATOMIC_SPECIES
>    Mg   24.30500  Mg.pz-bhs.UPF
>     B   10.81100  B.pz-bhs.UPF 
> ATOMIC_POSITIONS alat
>    Mg      0.000000000    0.000000000    0.000000000
>
>     B      0.500000000    0.288680000    0.570500000
>
>     B      0.000000000    0.577350000    0.570500000
>
> K_POINTS automatic 
>   30 30 30   1 1 1
> 
>
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