[Pw_forum] roblem with bfgs algorithm optimizer for spin polarized system

pc229 at kent.ac.uk pc229 at kent.ac.uk
Fri Mar 13 15:07:22 CET 2009


Thanks for the reply,
buT I am still thinking that should be a bug in the optimizer, since  I also tried to run my system like a metal and nothing gonna change. 
If I change the optimization method I can reach easly the convergence.
Cheers, Piero  

----- Original Message -----
From: Giuseppe Mattioli <giuseppe.mattioli at mlib.ism.cnr.it>
Date: Friday, March 13, 2009 11:21 am
Subject: Re: [Pw_forum] roblem with bfgs algorithm optimizer for spin	polarized system
To: PWSCF Forum <pw_forum at pwscf.org>

> 
> 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                
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> 
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