[Pw_forum] RE : Lattice Parameter too low from experimentally determined. (3.42 ~ 3.52)

[BARRETEAU Cyrille]

Dear Eliot

You should probably use a GGA pseudopotential (Ni.pz-nd-rrkjus.UPF is LDA) and also increase the number of kpoints (7 7 7 is too low especially for magnetic systems).

Cyrille

-----------------------------------------------------------------------------------------------------------
Cyrille Barreteau
CEA Saclay, IRAMIS, SPCSI, Bat. 462
91191 Gif sur Yvette Cedex, FRANCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
phone:    +33 (0)1 69 08 29 51 / +33 (0)6 47 53 66 52
fax :       +33 (0)1 69 08 84 46
email:     cyrille.barreteau at cea.fr
Web:     http://iramis.cea.fr/Pisp/cyrille.barreteau/
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________________________________________
De : pw_forum-bounces at pwscf.org [pw_forum-bounces at pwscf.org] de la part de Elliot Menkah [elliotsmenkah at yahoo.com]
Date d'envoi : mardi 3 décembre 2013 13:04
À : pw_forum at pwscf.org
Objet : [Pw_forum] Lattice Parameter too low from experimentally determined. (3.42 ~ 3.52)

Hi all,

I'm determining the lattice parameter of Nickel and my convergence test
is giving me 3.42 Angstroms against and experimentally determined 3.52.
Previous calculations by other people are showing 3.49 and 3.52
Angstroms as again.

What could be wrong with my parameters or calculations.

Below is the input file please.


#!/bin/sh
# check whether echo needs the -e option
#
executablepath=/home/molecular/espresso-5.0.2/bin/pw.x
for alat in  6.273 6.369 6.463 6.557 6.652 6.746 6.841 6.935
do
#input file
cat > Ni-$alat.in << EOF
&CONTROL
        title = 'Ni-ferro-mag' ,
        calculation = 'relax' ,
        restart_mode = 'from_scratch' ,
        outdir = './temp' ,
        pseudo_dir = '/home/molecular/Elliot/pseudo' ,
        prefix = 'Ni-ferromag',
        tstress = .true. ,
        tprnfor = .true. ,
/
  &SYSTEM
        ibrav = 2,
        celldm(1) = $alat,
        nat = 1,
        ntyp = 1,
        ecutwfc = 60,
        ecutrho = 480,
        occupations='smearing',
        smearing='fermi-dirac',
        degauss=0.003,
        nbnd=10
        nspin=2,
        starting_magnetization(1)=0.5,
/
  &ELECTRONS
         conv_thr = 1.0D-8
         mixing_beta = 0.2,
/
  &IONS
/
ATOMIC_SPECIES
         Ni1 58.6934   Ni.pz-nd-rrkjus.UPF
ATOMIC_POSITIONS (alat)
        Ni1       0.000000000   0.000000000   0.000000000
K_POINTS automatic
   7 7 7   0 0 0

EOF
$executablepath < Ni-$alat.in > Ni-$alat.out
grep "Final energy" Ni-$alat.out >> Ell0.txt
echo "$alat" >> Lat.txt
done
awk '{print $4}' Ell0.txt > Nel.txt
paste Lat.txt Nel.txt > Final_alat.txt

rm Lat.txt Ell0.txt


Thank uou.



Kind regards,

ELliot.

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