[Pw_forum] problem in calculating the binding energies with pwscf

[Jörg Buchwald]

Hello,
I'm performing some first test-calculations with pwscf, where I try to
get the binding energy of bulk silicon. The problem is, that the
resulting energy, which should be the difference of the total
energy of silicon crystal structure and the a free atom, is about 3eV
too low. I used different pseudopotentials, different
lattice-parameters and I also tested the convergencies (with k and
the energy-cut-off) which worked, but I don't have a clue what a made
wrong.

Here are my Input files:

---
 &control
    prefix='silicon',
    pseudo_dir='/home/joerg/espresso-4.3.1/pseudo'
    outdir = '/home/joerg/scratch',
 /
 &system
    ibrav=  2, celldm(1) =10.263142, nat=  2, ntyp= 1,
    ecutwfc = 30.0,
 /
 &electrons
 /
ATOMIC_SPECIES
 Si  28.086  Si.pbe-n-van.UPF
ATOMIC_POSITIONS
 Si 0.00 0.00 0.00
 Si 0.25 0.25 0.25
K_POINTS automatic
 9 9 9 1 1 1
---

and for the free atom:

---
&control
    prefix='silicon',
    pseudo_dir='/home/joerg/espresso-4.3.1/pseudo'
    outdir = '/home/joerg/scratch',
 /
 &system
    ibrav=  0, celldm(1) =50.2, nat=  1, ntyp= 1,
    ecutwfc = 80.0,occupations='fixed',starting_magnetization(1)=10,
 /
 &electrons
 /
ATOMIC_SPECIES
 Si  28.086  Si.pbe-n-van.UPF
ATOMIC_POSITIONS
 Si 0.50 0.50 0.50
K_POINTS gamma

CELL_PARAMETERS {cubic}
    1.00 0.00 0.00
    0.00 1.00 0.00
    0.00 0.00 1.00
---

It would be nice if someone could help me.
Thx & regards,
Jörg Buchwald


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