Re: [QE-users] Question about optimizing the lattice constant of iron

[Yi Wang]

Hi, Dear Gui Wei,

Using the PBE functional, the lattice constant of bcc Fe is supposed to be smaller than experimental value.

Please take a look at https://molmod.ugent.be/deltacodesdft. 

Wien2K gives 2.831 A. PSlib and GBRV give some value around 2.834.

And, PBE is one of the best functionals on bcc Fe.

As Stefano suggests, you might need to increase somehow the plane wave cutoff, though. (to reproduce other properties correctly) (and as well as the k-points)

Yi Wang

Tsinghua University

On 12/25/2018 18:02，Stefano de Gironcoli<degir...@sissa.it> wrote：

cutoff might be too small for a reliable computation of the stress.

other than that I see no big issue in your input

stefano

On 25/12/18 04:35, Gui Wei wrote:

Hi,

When optimizing the lattice constant of bcc Fe,the result is a=2.830A， which is in disagreement with experimentally derived structural parameter a=2.863A.Could someone give me some advice?

&CONTROL

    calculation = 'vc-relax'

    prefix='Fe1',

    pseudo_dir = '/public/home/duan1/gw2/pseudo/',

    outdir='/public/home/duan1/gw2/tempdir/'

    tprnfor     = .true.

    tstress     = .true.

/

&SYSTEM

    ibrav= 1, 

    A=2.8664

    nat= 2 

    ntyp= 1

    occupations='smearing',

    smearing='mp',

    degauss=0.02,

    ecutwfc =37

    ecutrho =240

    nspin   = 2

    starting_magnetization(1) = 0.4

/

&ELECTRONS

    conv_thr        = 1.0d-8

    mixing_beta      = 0.7

/

&IONS

   ion_dynamics = 'bfgs'

/

&CELL

   cell_dynamics = 'bfgs' 

/ 

ATOMIC_SPECIES

Fe  55.847  Fe.pbe-n-kjpaw_psl.0.2.4.UPF

ATOMIC_POSITIONS crystal

 Fe   0.0000000000000000   0.0000000000000000   0.0000000000000000

 Fe   0.5000000000000001   0.5000000000000001   0.5000000000000001

K_POINTS automatic

8  8  8  0  0  0

The result:

 CELL_PARAMETERS (alat=  5.41671099)

   0.987418499   0.000000000   0.000000000

   0.000000000   0.987418499   0.000000000

   0.000000000   0.000000000   0.987418499

Gui Wei

School of Mechanical Engineering，Chongqing University, China

_______________________________________________
users mailing list
users@lists.quantum-espresso.org
https://lists.quantum-espresso.org/mailman/listinfo/users

_______________________________________________
users mailing list
users@lists.quantum-espresso.org
https://lists.quantum-espresso.org/mailman/listinfo/users