[Pw_forum] converged to wrong magnetic state of hcp cobalt in Opteron

[Konstantin Kudin]

 Hi all,

 I'd like to point out that as long as the code converges to a proper
*local* minimum, all is OK. One cannot really expect that the code is
going to find the *global* minimum in a system where there are many
accessible low energy minima. The way things are implemented is to find
*a* minimum, not *the* minimum! Note that finding *the* minimum is a
quite tricky issue, and not a solved one.

 Different platforms (compilers/architectures) might have different
initial random wavefunctions, leading to different local minima. Is
that a sign of a problem? - Not at all!

 Until things improve, making sure that the electronic state obtained
is lowest in energy (i.e. the global minimum) is the operator's
responsibility.

 Kostya


--- wlyim at puccini.che.pitt.edu wrote:

> Dear Axel,
> 
> Thanks for your advice.
> 
> I have compiled pwscf.2.1.4 using EM64T Version 9.0 with MKL 8.0.1.
> Again, 
> the electronic structure went to the wrong state.
> ==================================================
> INTEL EM64T result:
> !    total energy              =  -148.81668356 ryd
>      estimated scf accuracy    <        2.0E-12 ryd
> 
>      band energy sum           =    15.05020564 ryd
>      one-electron contribution =     6.02718174 ryd
>      hartree contribution      =    21.83280277 ryd
>      xc contribution           =   -65.85608487 ryd
>      ewald contribution        =  -110.85073891 ryd
>      correction for metals     =     0.03015572 ryd
> 
>      total magnetization       =     3.75 Bohr mag/cell
>      absolute magnetization    =     4.14 Bohr mag/cell
> =======================================================
> 
> It seemed to me that in this chemical system, the energy is
> constantly
> shifted by 0.06 Ry when compared to Origin result. I pick up the
> first 
> iteration step for comparison:
> ================================================
> Origin:
>      iteration #  1     ecut=    30.00 ryd     beta=0.70
>      Davidson diagonalization (with overlap)
>      ethr =  1.00E-02,  avg # of iterations =  4.2
> 
>      npt with rhoup < 0:        2, npt tot    20736,      0.01 %
> 
>      npt with rhoup < 0:        2, npt tot    20736,      0.01 %
> 
>      total cpu time spent up to now is     15.75 secs
> 
>      total energy              =  -147.96340174 ryd
>      estimated scf accuracy    <     2.11694003 ryd
> 
>      total magnetization       =     5.92 Bohr mag/cell
>      absolute magnetization    =     5.97 Bohr mag/cell
> =================================================
> Opteron(PGI) or INTEL(EM64T) result:
>      iteration #  1     ecut=    30.00 ryd     beta=0.70
>      Davidson diagonalization (with overlap)
>      ethr =  1.00E-02,  avg # of iterations =  4.1
> 
>      npt with rhoup < 0:        2, npt tot    20736,      0.01 %
> 
>      npt with rhoup < 0:        2, npt tot    20736,      0.01 %
> 
>      total cpu time spent up to now is     30.39 secs
> 
>      total energy              =  -147.90474844 ryd
>      estimated scf accuracy    <     2.13792299 ryd
> 
>      total magnetization       =     5.95 Bohr mag/cell
>      absolute magnetization    =     6.00 Bohr mag/cell
> ======================================================
> 
> At the initial stage, I would expect that the "total energy" are
> quite 
> similar calculated in two different platforms. However this is not
> the 
> case. Origin's energy is about 0.06 Ry lower than that in Opteron.
> And 
> such a difference was kept till the end. I can't imagine what
> reasoned for 
> this. On the other hand, platinum is free of this problem.
> 
> Is it due to different fft treatments in Origin and Linux machines?
> Or 
> code/library problem?
> 
> Many thanks in advance.
> 
> Best regards,
> William
> 
> On Thu, 13 Apr 2006, Axel Kohlmeyer wrote:
> 
> > On Thu, 13 Apr 2006 wlyim at puccini.che.pitt.edu wrote:
> > 
> > WL> Dear all,
> > 
> > dear william,
> > 
> > please check the mailing list archives. the PGI compilers version
> 5.x
> > are _known_ to miscompile several parts of quantum espresso (and
> not
> > only that code, i know of several other DFT codes as well).
> > the same is true for quite few SGI compilers...
> > if you can, please try with the intel (EM64t) compilers on opteron
> > to check, whether it is still going to the wrong state. it
> additionally
> > may depend on the kind of BLAS/LAPACK library you are using. there
> are 
> > a few bugs in several of them as well.
> > 
> > best regards,
> >   axel.
> > 
> > WL> 
> > WL> I did a test on crystalline hcp cobalt by pwscf.2.1.4, both on
> Opteron
> > WL> (pgf90 5.2-4, lam 7.1.1) and Origin. I found that the
> calculation 
> > WL> converged to a wrong magnetic state in Opteron, while the
> calculation in 
> > WL> Origin was okay.
> > 
> > [...]
> > 
> > WL> I used the PBE uspp as provided in pwscf website. On the other
> hand, I 
> > WL> have also tried the calculations on platinum, which is a
> closed-shell 
> > WL> system, and I got essentially the same results from Opteron and
> Origin.
> > WL> 
> > WL> Does anyone experience a similar thing? I will be appreciated
> if someone 
> > WL> can give a help hand.
> > WL> 
> > WL> Many thanks in advance!
> > WL> 
> > WL> I am also attaching the input file at the bottom of this
> meesage.
> > WL> 
> > WL> regards,
> > WL> William
> > WL> 
> > 
> > [...]
> > 
> > 
> 
> 
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