[Pw_forum] roblem with bfgs algorithm optimizer for spin polarized system
Giuseppe Mattioli
giuseppe.mattioli at mlib.ism.cnr.it
Fri Mar 13 12:21:25 CET 2009
Dear Piero
> &ELECTRONS
> /
The default beta mixing parameter is often too high to fit for many purposes.
Try to use the keyword mixing_beta = 0.3 (e.g.) within the &electrons group.
> occupations = 'fixed' ,
This is not a good choice (at least in my experience) when you deal with
system in which the magnetization may change. Try to add a gaussian or a cold
smearing.
Yours
Giuseppe
On Friday 13 March 2009 01:23:46 pc229 at kent.ac.uk wrote:
> Dear PWscf developers,
> I am trying to optimize, on the latest version of the espresso code
> (v4.0.4 ), the cell parameter and also the ionic coordinate of hematite.
> Initially I treat hematite like an insulator using the following
> pseudo-potential :Fe.pbe-sp-van_ak.UPF for Iron and O.pbe-van_ak.UPF for
> oxygen (I attached the input at the bottom). To optimize both atomic
> coordinates and cell parameters I used bfgs algorithm . As you know
> hematite is an open-shell system, and you need to define the spin
> orientation in order to describe it like a ferro-magnetic or
> anti-ferromagnetic system. I choose the anti-ferromagnetic one, that means
> to have the total magnetization equal to 0 every SCF cycle and absolute
> magnetization ranging from 11-16 (this highly pseudo potential dependent).
> Anyway, for the first SCF cycle the magnetization carried out is correct,
> while after the first geometry optimization step hematite starts to lose
> the spin and the energy also dancing between two value not allowing the
> SCF to converge. So attempting to managed this problem I try to run it like
> a metal introducing a methfessel-paxton smearing. Nothing seems to
> change, the SCF of the second optimization step doesn't converge as
> previously. Then I tried to restart my calculation from the first point
> coordinates and the first SCF step converged, whilst the next no as in the
> previous cases . This is very strange and get me frustrated ! Then I run
> the same calculation changing both optimization algorithm to damp for the
> ionic coordinate and damp-w for the cell. In this way the SCFs after the
> first optimization cycle seem to converge with the right magnetization and
> the next as well. I did also a further trial, because I need to use the
> bfgs algorithm to optimize my structure. I tried to run the same system on
> a previous version of espresso (v.2.1.2), and treating it like a metal
> (with methfessel-paxton smering) and using bfgs for ionic coordinate and
> damp for cell optimization (since bfgs wasn't implemented to optimize the
> cell parameter in this version) the first SCF reached the convergence and
> the following as well. How can I solve it ? I also read in the documents
> related to PWscf that bfgs for optimizing cell parameters (vc-relax) is
> still in a experimental version. Would it be possible that It has some
> problem with spin polarized systems?? How can I manage this problem? I need
> desperately to use bfgs to optimize the hematite.
>
>
> Best Regards, Piero
>
>
> &CONTROL
> title = 'opt_bulk_PBE_van3.inp' ,
> calculation = 'vc-relax' ,
> restart_mode = 'from_scratch' ,
> wf_collect = .true. ,
> outdir =
> '/home/pc229/backup/Counts/PWscf/Fe2O3_bulk/PWSCF/Fe2O3_bulk/opt_bulk_PBE_v
>an/' , pseudo_dir =
> '/home/pc229/backup/Counts/PWscf/Fe2O3_bulk/PWSCF/Fe2O3_bulk/pseudo/' ,
> prefix = 'opt_bulk_PBE_van3.inp' ,
> /
> &SYSTEM
> ibrav = 5,
> celldm(1) = 11.091428,
> celldm(4) = 0.587237106,
> nat = 10,
> ntyp = 3,
> ecutwfc = 50 ,
> nosym = .true. ,
> nbnd = 70,
> nelec = 100,
> tot_charge = 0.000000,
> occupations = 'fixed' ,
> nspin = 2 ,
> starting_magnetization(1) = 1.,
> starting_magnetization(2) = -1.,
> starting_magnetization(3) = 0.,
> tot_magnetization = 0 ,
> /
> &ELECTRONS
> /
> &IONS
> ion_dynamics = 'bfgs' ,
> /
> &CELL
> cell_dynamics = 'bfgs' ,
> wmass = 2001.0060 ,
> cell_dofree = 'all' ,
> /
> ATOMIC_SPECIES
> Fe 55.62000 Fe.pbe-sp-van_ak.UPF
> Fe1 55.62000 Fe.pbe-sp-van_ak.UPF
> O 15.99000 O.pbe-van_ak.UPF
> ATOMIC_POSITIONS crystal
> Fe 0.144358141 0.144342247 0.144393006
> Fe1 0.355605889 0.355642696 0.355656118
> Fe1 0.644394003 0.644359012 0.644344959
> Fe 0.855641399 0.855655859 0.855605070
> O 0.556470421 0.943529173 0.250007053
> O 0.250006034 0.556470770 0.943529639
> O 0.943529367 0.250006711 0.556470944
> O 0.443532949 0.056467967 0.749992942
> O 0.749994148 0.443532454 0.056467520
> O 0.056467649 0.749993110 0.443532750
> K_POINTS automatic
> 4 4 4 0 0 0
>
>
> --
> Pieremanuele Canepa
> Room 230
> School of Physical Science
> Ingram Building
> University of Kent,
> Canterbury,
> Kent, CT2 7NH
> United Kingdom
> Cell: +44-7768685833
> ID Skype: pieremanuele
> ID msn: pieremanuele83 at hotmail.com
> --------------------------------------------------------
--
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Giuseppe Mattioli
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
v. Salaria Km 29,300 - C.P. 10
I 00016 - Monterotondo Stazione (RM)
Tel + 39 06 90672836 - Fax +39 06 90672316
E-mail: <giuseppe.mattioli at ism.cnr.it>
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