[Wien] please help

[Peter Blaha]

As I said in my previous mail:

A paramagnetic state of a 4f compound does NOT mean that one should do a
unpolarized calculation.
Even in the paramagnetic case, one has local moments on each Gd site, but
they are no longer long range ordered, but randomly oriented, thus there
is no net magnetization.

Eventually you can try the effects of magnetic disorder and flip the spins
on two Gd atoms in your supercell (so that the net moment of the cell is again
zero, but you do not have the strict AF state anymore.

PS: I'd expect a rather small influence on the EFG on Cd by that. Other effects
(lattice expansion and phonons) may play a role too.

susanta mohanta schrieb:
> Dear Prof Peter Blaha,
> I have calculated spin polarised calculation in Gd(2*2*2)for Cd
> impurity and the results,hyperfine field, magnetic moment,electric
> field gradient reasonably matches with available literature.actually
> I am interested to find out the electric field gradient of Cd in Gd at room
> temperature which is paramagnetic, and thats why I have started unpolarised
> calculation,and faced the problem.So how to proceed in this regard?
> 
> with regards
> Susanta kumar Mohanta
> 
> 
> On Tue, Sep 16, 2008 at 10:51 AM, Peter Blaha 
> <pblaha at theochem.tuwien.ac.at <mailto:pblaha at theochem.tuwien.ac.at>> wrote:
> 
>     I'm not surprised that a Gd-supercell does NOT converge in an
>     unpolarized calculation.
> 
>     You have to consider the underlying physics: Gd metal has 7 4f
>     electrons, thus in a polarized calculation this gives a rather stable
>     situation, i.e. "all" 7 spin-up states are occupied, but all 7 spin-dn
>     states empty.
>     In an unpolarized case you must put 7 electrons into "3.5 states" (each
>     state takes now 2 electrons!) and it is rather naturally that this will
>     cause problems.
> 
>     The VERY efficient mixer seems to manage this for pure Gd, but in the
>     supercell there are many more degrees of freedom and thus convergence is
>     much more difficult. Eventually, switching to TEMP and a rather large
>     broadening will help to converge.
> 
>     In any case, you have to ask yourself: what should this calculation be
>     good for ?? Even above the Neel/Curie-point one has local magnetic
>     moments (only the long range order has gone).
> 
>     susanta mohanta schrieb:
>      >
>      > Dear all,
>      >
>      > I have finished spin polarised calculation for Gd(2*2*2
>     supercell) with Cd
>      > impurity.But When I started with same structure for unpolarised
>     calculation
>      > with RKMAX=7.5:GMAX=14 and 300kpoints(to begin with),the computation
>      > doesn;t seems to converge.After 200 cycle we noticed that both
>     charge and
>      > energy are oscillating.So please help me in this regard.I have also
>      > calculated
>      > unpolarised calculation for pure Gd.So what may be the problem?
>      >
>      > with regards
>      > susanta
>      >
>      > --
>      > SUSANTA K MOHANTA
>      > RESEARCH SCHOLAR
>      > DEPT.OF PHYSICS
>      > IIT KHARAGPUR
>      > *****************************
>      >
>      >
>      >
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> 
> 
> 
> -- 
> SUSANTA K MOHANTA
> RESEARCH SCHOLAR
> DEPT.OF PHYSICS
> IIT KHARAGPUR
> *****************************
> 
> 
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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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