[Pw_forum] problem in calculating the binding energies with pwscf

[Jörg Buchwald]

Hi,
Thx, now it looks much better. I set the starting_magnetization to 10
only for test reasons, but as you said, it was the wrong switch.
Regards,
Jörg

--
Leibniz-Institut fuer Oberflaechenmodifizierung e.V.
Permoserstrasse 15
04318 Leipzig
GERMANY


Am Thu, 21 Jul 2011 11:13:43 -0400 (EDT)
schrieb elbuesta at icqmail.com:

> 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: Jörg Buchwald <joerg.buchwald at iom-leipzig.de>
> 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,
> Jörg Buchwald
> 
> 
> Leibniz-Institut fuer Oberflaechenmodifizierung e.V.
> Permoserstrasse 15
> 04318 Leipzig
> GERMANY
> 
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