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

[Elliot Menkah]

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.