[Pw_forum] Re hubbard U and stable structure
Gabriele Sclauzero
sclauzer at sissa.it
Mon May 18 15:07:46 CEST 2009
Naol Regassa wrote:
> Dear GS
>
> Thank you for responding to my question.
> In my question I said "more effective" because I seen some changes on
> the band structure of cubic ferromagnetic by adding U.But not as
> effective ( it won't make totally an insulator) as the one I have seen
> on the (experimentally found) stable structure i.e. hexagonal.
To figure it out maybe you can have a look at the PDOS in the two cases. The U term
changes the position of the Mn states and consequently the bands which come from an
hybridization between Mn states and other states. You should understand between which kind
of states the gap forms by projecting your bands onto the atomic wavefunctions (use
projwfc.x for this).
HTH
GS
>
>
> On 5/18/09, pw_forum-request at pwscf.org <pw_forum-request at pwscf.org> wrote:
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>> Today's Topics:
>>
>> 1. Re: Hubbard U and small degauss ... (Gabriele Sclauzero)
>> 2. Electron-Phonon: loading dVscf file when ldisp=.TRUE.
>> (Andrea Marini)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Mon, 18 May 2009 10:12:25 +0200
>> From: Gabriele Sclauzero <sclauzer at sissa.it>
>> Subject: Re: [Pw_forum] Hubbard U and small degauss ...
>> To: PWSCF Forum <pw_forum at pwscf.org>
>> Message-ID: <4A111869.30202 at sissa.it>
>> Content-Type: text/plain; charset=us-ascii; format=flowed
>>
>> Dear Naol,
>>
>> Naol Regassa wrote:
>>> Dear all
>>>
>>> I have two questions to ask
>>>
>>> a) For the last times I was calculating the effect of Hubbard U on the
>>> system YMnO_3 using QESPRESSO 4.10. I got an insulator band structure
>>> using U = 10.5eV though it is completely metal without U (GGA). When I
>> This is plausible. Though I don't know the physics of your compound, I can
>> tell you that
>> for simpler transition metal oxides (like FeO) you find the same change
>> (i.e. from metal
>> to insulator) after introducing the Hubbard U. Please have a look at Matteo
>> Cococcioni's
>> PhD thesis (from http://www.sissa.it/cm/phd.php) and the related paper (PRB
>> 2005).
>>
>>> got this result I have used small degauss = 0.006. My friend told me
>>> to use degauss = 0.015.
>> Have you asked him the reason? I don't see any...
>>
>> In principle you should test convergence of the total energy (and other
>> quantities you're
>> interested in) w.r.t all the parameters which introduce significant
>> approximations to your
>> result. As you decrease degauss you'll reach the correct result for your
>> system at T=0
>> (chosing k-point grids accordingly), so I don't see any reason to choose
>> higher degauss
>> other that saving computer time.
>>
>> In the specific case of DFT+U, you have to be carefull to converge the local
>> occupations
>> too. They are very sensitive to the value of ecutwfc, but also degauss and
>> number k-points
>> have to be checked.
>>
>> Please tell me how possible (correct) is
>>> that? I checked the convergence for degauss but it is increasing near
>>> 0.015.
>> What is increasing?
>>
>>
>>> b) Is adding U value more effective for the most stable structure ?
>> Sorry I cannot get this question... in which sense "more effective"?
>>
>>> For the unstable states like for my case cubic ferromagnetic phase I
>>> can't see any change?
>> What are looking at? Maybe your question is clear to someone who's studying
>> systems like
>> yours, so it's because of me that I cannot get the point... but if you could
>> be more
>> precise maybe you would have more change to get help.
>>
>>
>> Regards,
>>
>>
>> GS
>>
>>
>>
>>> Here is the input for the 'scf'
>>> &control
>>> calculation = 'scf',
>>> restart_mode = 'from_scratch',
>>> prefix = 'ymo_hcp_ferro'
>>> tstress = .true.,
>>> tprnfor = .true.,
>>> pseudo_dir = '/home/MSC608/Desktop/QESPRESSO_PP',
>>> outdir='/home/MSC608/Thesis/Hexagonal/Ferro-Hex/temp'
>>> /
>>> &system
>>> ibrav = 0,
>>> celldm(1) = 6.7,
>>> nat = 10,
>>> ntyp = 4,
>>> ecutwfc = 32,
>>> ecutrho = 340.0
>>> nspin = 2
>>> starting_magnetization(2) = 0.7,
>>> starting_magnetization(3) = 0.7,
>>> occupations = 'smearing',
>>> smearing = 'marzari-vanderbilt',
>>> degauss = 0.005,
>>> lda_plus_u=.true.,
>>> Hubbard_U(2) = 10.5,
>>> Hubbard_U(3) = 10.5,
>>> /
>>> &electrons
>>> diagonalization = 'david'
>>> startingwfc = 'atomic+random'
>>> mixing_beta = 0.3,
>>> conv_thr = 1.0d-10
>>> /
>>> ATOMIC_SPECIES
>>> Y 88.91 Y.pbe-nsp-van.UPF
>>> Mn1 54.94 Mn.pbe-sp-van_mit.UPF
>>> Mn2 54.94 Mn.pbe-sp-van_mit.UPF
>>> O 15.9994 O.pbe-rrkjus.UPF
>>>
>>> CELL_PARAMETERS (alat)
>>> 0.985236441 -0.266531554 -0.000316189
>>> -0.266366323 0.985859979 0.000349871
>>> 0.000781869 -0.000890980 3.186836665
>>>
>>> ATOMIC_POSITIONS (crystal)
>>> Y -0.082663260 -0.082649328 0.000174846
>>> Y -0.082874577 -0.082880779 0.499813069
>>> Mn1 0.205305857 0.560245090 0.249986248
>>> Mn2 0.561457263 0.207812583 0.750012603
>>> O -0.027464907 -0.056329933 0.249979343
>>> O -0.058482388 -0.031289340 0.750035308
>>> O 0.247951998 0.582250730 0.083800805
>>> O 0.582338704 0.248188482 0.916046842
>>> O 0.582135578 0.247948396 0.583964864
>>> O 0.247742343 0.582041831 0.416186070
>>> K_POINTS automatic
>>> 3 3 2 1 1 1
>>>
>>> Thanks alot in advance
>>> Tamene Regassa
>>> AAU
>>> Ethiopia
>>> _______________________________________________
>>> Pw_forum mailing list
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>> --
>>
>>
>> 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 |
>> o ------------------------------------------------ o
>>
>>
>> ------------------------------
>>
>> Message: 2
>> Date: Mon, 18 May 2009 10:09:58 +0200 (CEST)
>> From: Andrea Marini <Andrea.Marini at roma2.infn.it>
>> Subject: [Pw_forum] Electron-Phonon: loading dVscf file when
>> ldisp=.TRUE.
>> To: Pw_forum at pwscf.org
>> Message-ID:
>> <alpine.LFD.2.00.0905180949290.25064 at anomaly.roma2.infn.it>
>> Content-Type: text/plain; charset="us-ascii"
>>
>> Dear all,
>>
>> I am encountering a problem when calculating lambda constants
>> (PH/elephon.f90). Till now I used to
>>
>> 1. calculate first phonons and dVscf file by using
>>
>> elph=.false.,
>> trans=.true.,
>> ldisp=.false.,
>>
>> in the ph.x input file.
>>
>> 2. re-read the dvscf file using a larger k-point grid and changing in the
>> ph.x input file
>>
>> elph=.true.,
>> trans=.false.,
>> ldisp=.false.,
>>
>> This method works great. If I compare the result of point 2 against the
>> calculation 1 using elph=.true. the lambda factors are identical.
>>
>> Now I am trying to follow points 1 and 2 when ldisp=.TRUE.. Here the
>> results of the calculation 2, when the dVscf file is read from disk, are
>> different the case when phonons and lambda's are calculated in the same
>> run.
>> More importantly I get that the symmetry of the lambda factors are not
>> respected for some q-points when the dVscf file is read from disk:
>>
>> < ldisp=.true., trans=.true., elph=.true.
>>> ldisp=.true., trans=.false., elph=.true.
>> < q = ( 0.500000000 -0.500000000 0.500000000 )
>> <
>> < omega( 1) = 3.751393 [THz] = 125.133833 [cm-1]
>> < omega( 2) = 3.751393 [THz] = 125.133833 [cm-1]
>> < omega( 3) = 9.121952 [THz] = 304.277585 [cm-1]
>> <
>>
>> < lambda( 1)= 2.6170 gamma= 1077.54 GHz
>> < lambda( 2)= 2.6170 gamma= 1077.54 GHz
>> < lambda( 3)= 0.1901 gamma= 462.75 GHz
>> ---
>>> lambda( 1)= 31.9820 gamma=13168.61 GHz
>>> lambda( 2)= 23.5894 gamma= 9712.95 GHz
>>> lambda( 3)= 19.7009 gamma=47963.51 GHz
>>
>> Maybe I am doing something wrong. I would really appreciate is someone
>> could help me.
>>
>> I have attached to this mail a tar.gz file with all inputs to reproduce
>> the above described error in the simple case of Al bulk. All the runs take
>> less than 5 minutes. I have already created all the links so if you want
>> to try, simple
>>
>>> cd Alluminum_TEST/
>>> cd CALCULATE_DVSCF_LDISP_TRUE/
>>> pw.x < gs.in > gs.out
>>> ph.x < ph.in > ph.out
>>> cd ../READ_DVSCF_LDISP_TRUE/
>>> pw.x < gs.in > gs.out
>>> ph.x < ph.in > ph.out
>>> cd CALCULATE_DVSCF_SINGLE_Q/
>>> pw.x < gs.in > gs.out
>>> pw.x < nscf.in > nscf.out
>>> ph.x < ph.in > ph.out
>>> cd READ_DVSCF_SINGLE_Q
>>> pw.x < gs.in > gs.out
>>> pw.x < nscf.in > nscf.out
>>> ph.x < ph.in > ph.out
>> The diff between the files CALCULATE_DVSCF_LDISP_TRUE/ph.out and
>> READ_DVSCF_LDISP_TRUE/ph.out is saved as DIFF_LDISP_TRUE.
>>
>> Cheers
>>
>> Andrea
>>
>> --------------------------------------------------------------------------
>> Andrea MARINI
>>
>> Physics Department, University of Rome "Tor Vergata" (Italy)
>> - phone: +39-0672594894 - fax: +39-062023507 -
>>
>> - andrea.marini at roma2.infn.it -- http://www.yambo-code.org/people/andrea -
>> -------------- next part --------------
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--
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 |
o ------------------------------------------------ o
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