[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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