[Pw_forum] RE : RE : A question on atomic magnetic moments

[BARRETEAU Cyrille]

Dear Giovani
 
I personnaly did calculations on Fe clusters some time ago. I always found "almost integer" magnetic moments.
However I once encoutered some difficulties with the default  value of "nbnd". I had to increase it. Try to set nbnd=20 for example...
 
Magnetic clusters can be very tricky.. It also very common to find several magnetic solutions..
 
good luck
 
 cyrille
 
================================================================== 
Cyrille Barreteau                                                      phone : +33 (0)1 69 08 29 51 
CEA Saclay                                                             fax :      +33 (0)1 69 08 84 46 
IRAMIS, SPCSI,    Batiment 462                            email     cyrille.barreteau at cea.fr 
91191 Gif sur Yvette Cedex 
FRANCE 
~~~~~~~~~~~~~~~~~~~~~~~~ 
Web: http://iramis.cea.fr/Pisp/cyrille.barreteau/ 
==================================================================

________________________________

De: pw_forum-bounces at pwscf.org de la part de Giovani Faccin
Date: lun. 14/02/2011 05:50
À: PWSCF Forum
Objet : Re: [Pw_forum] RE : A question on atomic magnetic moments


Dear Cyrille,

First of all, thanks for the reply on my post.

Following your suggestion, I've run a few calculations with lower degauss values. In particular, the ones reported on the message for Duy Le were made with a much smaller value ( 0.005 ) than the original 0.02 from the first message. Besides that, I've tried degauss values as low as 0.002 without any significant improvement on the final magnetization. 

I'm still wondering how do people find 6.00 so easily for the magnetization. I'm trying with 2 different DFT codes and no way I'm reaching those results, even though bulk/dimer equilibrium distances and force constants appear to be ok.

Any other ideas, just tell me, I'll try it and report back on the list.

Thanks again,

Giovani



2011/2/13 BARRETEAU Cyrille <cyrille.barreteau at cea.fr>


	Dear Giovani
	Try to decrease the degauss value of your smearing.. and see what happens.
	
	 cyrille
	
	
	==================================================================
	Cyrille Barreteau                                                      phone : +33 (0)1 69 08 29 51
	CEA Saclay                                                             fax :      +33 (0)1 69 08 84 46
	IRAMIS, SPCSI,    Batiment 462                            email     cyrille.barreteau at cea.fr
	91191 Gif sur Yvette Cedex
	FRANCE
	~~~~~~~~~~~~~~~~~~~~~~~~
	Web: http://iramis.cea.fr/Pisp/cyrille.barreteau/
	==================================================================
	
	________________________________
	
	De: pw_forum-bounces at pwscf.org de la part de Giovani Faccin
	Date: dim. 13/02/2011 07:16
	À: PWSCF Forum
	Objet : Re: [Pw_forum] A question on atomic magnetic moments
	
	
	Dear Paolo,
	
	Thanks for the reply.
	
	Just to make sure that the simulation cell size is not an issue (so that the system is really finite), I've tested different possibilities, including some quite big cells. Still, after a certain size the value of the magnetization is converging to 6.82 instead of the expected 6.
	
	So something else is causing this. Unfortunately I've got no clue as to what could it be.
	
	Should it be of any help, this is my input file:
	
	
	 &CONTROL
	                calculation = 'scf' ,
	               restart_mode = 'from_scratch' ,
	                 wf_collect = .true. ,
	                     outdir = './output' ,
	                 pseudo_dir = '../pseudo/' ,
	                     prefix = 'fe' ,
	              etot_conv_thr = 1.0D-9 ,
	              forc_conv_thr = 1.0D-6 ,
	                    tstress = .true. ,
	                    tprnfor = .true. ,
	 /
	 &SYSTEM
	                      ibrav = 1,
	                  celldm(1) = 43,
	                        nat = 2,
	                       ntyp = 1,
	                    ecutwfc = 100 ,
	                    ecutrho = 300 ,
	                occupations = 'smearing' ,
	                    degauss = 0.02 ,
	                   smearing = 'methfessel-paxton' ,
	                      nspin = 2 ,
	  starting_magnetization(1) = 1.0,
	 /
	 &ELECTRONS
	                   conv_thr = 1.0e-9 ,
	                mixing_beta = 0.7 ,
	            diagonalization = 'david' ,
	 /
	ATOMIC_SPECIES
	  Fe   58.69000  Fe.pbe-nd-rrkjus.UPF
	ATOMIC_POSITIONS angstrom
	  Fe      0.000000000    0.000000000    0.000000000
	  Fe      2.047510       0.000000000    0.000000000
	K_POINTS automatic
	 1 1 1   1 1 1
	
	Any suggestions are highly welcome.
	
	Giovani
	
	
	
	2011/2/12 Paolo Giannozzi <giannozz at democritos.it>
	
	
	
	       On Feb 11, 2011, at 17:09 , Giovani Faccin wrote:
	
	       > My question: shouldn't those numbers be integers?
	
	
	       only in finite systems, if you neglect spin-orbit.
	
	       P.
	       ---
	       Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
	       Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
	       Phone +39-0432-558216, fax +39-0432-558222
	
	
	
	
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	Giovani
	
	
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