[Pw_forum] How to compute the average Coulomb repulse U and exchange parameter J

clie clie at aphy.iphy.ac.cn
Thu Apr 16 16:10:30 CEST 2009


Dear friends,
Have you ever computed the average Coulomb repulse U and exchange parameter J
by pwscf. Could someone give some more detailed explanation about how to
process the output to get the U and J. I have read this pape(PHYSICAL REVIEW B
71, 035105, 2005), but I am still confusing about how to get U. Thank you in
advance.
All the best,
Zhi Li

-----------------------------------------------
Ex5 group Extreme Condition Physics, Institute of Physics, Chinese
Academy of Sciences, P. O. Box 603, Beijing, 100190, People’s Republic of
China



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>    1. Re: Convergence Problem (??)
>    2. Re: Convergence Problem (??)
>    3. Re: Convergence Problem (Prasenjit Ghosh)
>    4. Re: Convergence Problem (Gabriele Sclauzero)
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> ----------------------------------------------------------------------
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> Message: 1
> Date: Thu, 16 Apr 2009 11:31:53 +0800
> From: ?? <panda.deng.pan at gmail.com>
> Subject: Re: [Pw_forum] Convergence Problem
> To: PWSCF Forum <pw_forum at pwscf.org>
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> maybe the ecutwfc value is small.
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> Message: 2
> Date: Wed, 15 Apr 2009 22:42:42 -0500
> From: ?? <sunyang198498 at gmail.com>
> Subject: Re: [Pw_forum] Convergence Problem
> To: PWSCF Forum <pw_forum at pwscf.org>
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> Thanks for your advice, Deng.
> 
> Yang
> 
> 2009/4/15 ?? <panda.deng.pan at gmail.com>:
>> maybe the ecutwfc value is small.
>>
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> 
> 
> -- 
> University of Nebraska at Lincoln
> 
> 
> ------------------------------
> 
> Message: 3
> Date: Thu, 16 Apr 2009 07:57:38 +0200
> From: Prasenjit Ghosh <prasenjit.jnc at gmail.com>
> Subject: Re: [Pw_forum] Convergence Problem
> To: PWSCF Forum <pw_forum at pwscf.org>
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> Hi Yang,
> 
> Here are a few general suggestions:
> 
> (1) Check the convergence wrt to vacuum (distance between periodic images).
> In ur case it seems too small to me, as a result of which the periodic
> images are interacting. I think this is specially important for ur case
> because ur having an external electric field.
> 
> (2) check convergence wrt ecutrho & ecutwfc. Ususally ecutrho is 10-12 times
> ecutwfc. (probably ur wave fn is not converged)
> 
> (3) a value of mixing beta=0.05 is too low. Such a low value often implies
> that you don't move the electrons at all......hence its not very
> effective........according to my experience,  at least for cal. without
> electric field, a value of 0.2-0.3 works well.
> 
> (4) Also you are doing a slab cal. and usually either a few layers at the
> bottom or a few in the middle are kept fixed (although this should not
> affect ur electronic minimization).
> 
> With regards,
> Prasenjit.
> 
> 
> 
> (5) ur value of conv_thr seem too high.....at least u should use the default
> value. But I would suggest u to use something of the order of 10^-8.
> 
> 2009/4/16 ?? <sunyang198498 at gmail.com>
> 
>> Thanks for your advice, Deng.
>>
>> Yang
>>
>> 2009/4/15 ?? <panda.deng.pan at gmail.com>:
>> > maybe the ecutwfc value is small.
>> >
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>>
>> --
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> 
> 
> -- 
> PRASENJIT GHOSH,
> POST-DOC,
> ROOM NO: 265, MAIN BUILDING,
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> Message: 4
> Date: Thu, 16 Apr 2009 08:43:06 +0200
> From: Gabriele Sclauzero <sclauzer at sissa.it>
> Subject: Re: [Pw_forum] Convergence Problem
> To: PWSCF Forum <pw_forum at pwscf.org>
> Message-ID: <49E6D37A.1090506 at sissa.it>
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> 
> On top of what alreay said by the other users, I would suggest few more
things:
>> Below is the input file. Any suggestion is highly appreciated.
>> 
>> 
>> 
>> 
>> &control
>>     calculation='scf'
>>     restart_mode='from_scratch',
>>     pseudo_dir = '$PSEUDO_DIR/',
>>     outdir='$TMP_DIR/'
>>     prefix='Pd'
>>     tefield = .true.
>>     dipfield = .true.
>>     nstep = 300
>> 
>>  /
>>  &system
>>     ibrav = 6
>>     celldm(1) = 7.3331
>>     nspin = 2
>>     celldm(3) = 4.5
>>     edir = 3
>>     emaxpos=0.72
>>     eopreg=0.28
>>     eamp = -0.001944
> 
> I don't know much about efield calculations, but I suppose that you are sure
that you 
> placed the discontinuity of the potential in the vacuum, as should be done.
> 
>>     starting_magnetization=0.05
> 
> To be rigorous, starting_magnetization is a vector. In order to avoid strange
surprises, 
> you should specify
>     starting_magnetization(1)=0.05
>     ...
> 
>>     ntyp = 1
>>     nat= 14
>>     ecutwfc = 25.0,
>>     ecutrho = 500.0,
>>     occupations='smearing',
>>     degauss=0.2
> 
> This value of degauss (which is in Ryd, NOT eV) seems exceedingly high to me.
I would use 
> something like at least 1 order of magnitude smaller (but you should test
convergence by 
> yourself, together with the k-point mesh).
> 
> You may also want to try different kind of smearing methods. Methfessel-
Paxton usually 
> works well with metals (smearing="mp")
> 
>>     nbnd=160
> 
> Usually there is no need to specify the number of bands when using smearing.
The number of 
> bands which will be computed is automatically increased by the program to a
safe choice.
> 
>>  /
>> 
>>  &electrons
>>     conv_thr = 1.0e-4
> 
> See Ghosh's reply...
> 
>>     mixing_mode='local-TF'
> 
> have you tried a different mixing mode? I don't know if this is well suited
for slab 
> calculations.
> 
> 
> HTH
> 
> GS
> 
>>     mixing_beta = 0.05
>>     mixing_ndim = 12
>> 
>>  /
>> ATOMIC_SPECIES
>>  Pd  100  Pd.pz-nd-rrkjus.UPF
>> ATOMIC_POSITIONS
>> Pd       0.500000000   0.000000000  -1.496126804
>> Pd       0.000000000   0.500000000  -1.496126804
>> Pd       0.000000000   0.000000000  -1.002542052
>> Pd       0.500000000   0.500000000  -1.002542051
>> Pd       0.500000000   0.000000000  -0.501470158
>> Pd       0.000000000   0.500000000  -0.501470158
>> Pd       0.000000000   0.000000000   0.000000000
>> Pd       0.500000000   0.500000000   0.000000000
>> Pd       0.500000000   0.000000000   0.501470158
>> Pd       0.000000000   0.500000000   0.501470158
>> Pd       0.000000000   0.000000000   1.002542052
>> Pd       0.500000000   0.500000000   1.002542051
>> Pd       0.500000000   0.000000000   1.496126804
>> Pd       0.000000000   0.500000000   1.496126804
>> 
>> 
>> 
>> 
>> K_POINTS (automatic)
>>  8 8 1 0 0 0
>> 
>> 
>> 
> 
> -- 
> 
> 
> o ------------------------------------------------ o
> | Gabriele Sclauzero, PhD Student                  |
> | c/o:   SISSA & CNR-INFM Democritos,              |
> |        via Beirut 2-4, 34014 Trieste (Italy)     |
> | email: sclauzer at sissa.it                         |
> | phone: +39 040 3787 511                          |
> | skype: gurlonotturno                             |
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