[Pw_forum] problem in calculating the binding energies with pwscf

[Hongsheng Zhao]

On 07/21/2011 11:13 PM, elbuesta at icqmail.com wrote:
> Hello Joerg Buchwald,
>
> a few comments. Starting magnetization should be between -1 and 1. 1

Why not between -1 and 1?  Any hints?

> 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.

What do you mean by saying "spin unrestricted calculations", I have 
little experience on magnetic calculations, could you please give me 
some hints?

> Only starting magnetization does not do anything.
>
> In addition, I wouldn't compare the energy of the bulk and the isolated
> atom this way

Then, what's you way for this issue, any hints?

> 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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-- 
Hongsheng Zhao <zhaohscas at yahoo.com.cn>
School of Physics and Electrical Information Science,
Ningxia University, Yinchuan 750021, China