Hello Joerg Buchwald,
a few comments. Starting magnetization should be between -1 and 1. 1 means that
all available electrons from the PP have spin up. Also, if you want to do spin
unrestricted calculations, you should set nspin=2. Only starting magnetization
does not do anything.
In addition, I wouldn't compare the energy of the bulk and the isolated atom
this way because the cutoff on the WFC is quite different for each case: energy
differences converge much faster than the total energy. But I don't think that
is the problem here, only the magnetization is.
I slightly modified your inputs and got 4.5eV. If I remember well, this value
is okay. I hope it helps. All best!
Free Si atom:
&control
prefix='si_free',
pseudo_dir='/home/alex/pseudo'
outdir = '/scratch/alex',
/
&system
ibrav= 1, celldm(1) =25, nat= 1, ntyp= 1,
ecutwfc =
30.0,occupations='fixed',nspin=2,tot_magnetization=2.,nosym=.true.,
/
&electrons
/
ATOMIC_SPECIES
Si 28.086 Si.pbe-n-van.UPF
ATOMIC_POSITIONS
Si 0.50 0.50 0.50
K_POINTS gamma
......................................
Bulk Si:
&control
prefix='silicon',
pseudo_dir='/home/alex/pseudo'
outdir = '/scratch/alex',
/
&system
ibrav= 2, celldm(1) =10.263142, nat= 2, ntyp= 1,
ecutwfc = 40.0,
/
&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
................................................................
-----Original Message-----
From: J?rg Buchwald <[email protected]>
To: pw_forum <pw_forum at pwscf.org>
Sent: Thu, Jul 21, 2011 3:15 pm
Subject: [Pw_forum] problem in calculating the binding energies with pwscf
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,
J?rg Buchwald
Leibniz-Institut fuer Oberflaechenmodifizierung e.V.
Permoserstrasse 15
04318 Leipzig
GERMANY
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