[Pw_forum] Wrong occupation number for f electrons

[Paolo Giannozzi]

It is not always easy to get the occupation numbers right 
(and in general, to get the correct behavior) in f-electron 
systems. Maybe DFT Gd doesn't like to be ferromagnetic?

P.

On Fri, 2013-03-29 at 16:03 -0400, 琨陶 wrote:
> Dear everyone,
> 
> I want to calculate the magnetic properties of bulk Gd which contains
> two Gd atoms in the unit cell. In the input files, I set two Gd atoms
> to be ferromagnetic configuration. I searched the occupation number
> for each atom In the output file, and found following information:
> 
> At the beginning:
> 
> atom    1   Tr[ns(na)] (up, down, total) =   7.00000  0.00000  7.00000
> atom    2   Tr[ns(na)] (up, down, total) =   7.00000  0.00000  7.00000
> 
> However, after the first iteration, I found the occupation number of
> the first atom is totally wrong as following:
> 
> atom    1   Tr[ns(na)] (up, down, total) =   7.00064  5.60439 12.60503
> atom    2   Tr[ns(na)] (up, down, total) =   6.87289  0.00836  6.88125
> 
> At the last iteration, I found:
> 
> atom    1   Tr[ns(na)] (up, down, total) =   3.60781  3.88818  7.49599
> atom    2   Tr[ns(na)] (up, down, total) =   7.00165  0.09767  7.09932
> 
> 
> But, when I changed these two Gd atoms to be antiferromagnetic case,
> both of them had correct occupation number as fellowing:
> 
> atom    1   Tr[ns(na)] (up, down, total) =   7.00000  0.00000  7.00000
> atom    2   Tr[ns(na)] (up, down, total) =   0.00000  7.00000  7.00000
> atom    1   Tr[ns(na)] (up, down, total) =   7.00291  0.02028  7.02319
> atom    2   Tr[ns(na)] (up, down, total) =   0.00924  7.00258  7.01182
> atom    1   Tr[ns(na)] (up, down, total) =   7.00130  0.12233  7.12362
> atom    2   Tr[ns(na)] (up, down, total) =   0.11939  7.00128  7.12068
> 
> 
> Could you give me some suggestions? Any advices are highly
> appreciated!
> 
> 
> With regards,
> 
> Kun Tao
> 
> 
> 
> PS: The following is the input file:
> 
> 
>  &control
>     calculation='scf'
>     restart_mode='from_scratch',
>     prefix='Gd',
>     pseudo_dir = './'
>     outdir='./',
>  /
>  &system
>     ibrav= 4, celldm(1)= 6.96, celldm(3)= 1.59,
> 
>     nat= 2, ntyp=2,
>     nspin = 2,
>     starting_magnetization(1)=1.0,
>     starting_magnetization(2)=1.0,
> 
>     ecutwfc=55.0,
>     ecutrho=220.0,
>     occupations ='smearing',
>     smearing ='gauss',
>     degauss = 0.01,
> 
>     lda_plus_u = .true.
>     Hubbard_U(1)= 1.d-20
>     Hubbard_U(2)= 1.d-20
> 
>  /
>  &electrons
>     diagonalization='david',
>     mixing_beta = 0.3,
> 
>     conv_thr = 1.0d-6,
>     electron_maxstep = 400,
>  /
> ATOMIC_SPECIES
>  Gd1  1.0  Gd.GGA-PBE-paw.UPF
> 
>  Gd   1.0  Gd.GGA-PBE-paw.UPF
> ATOMIC_POSITIONS {crystal}
> 
> Gd1  0.00000000  0.00000000  0.00
> Gd   0.33333333 -0.33333333  0.50
> K_POINTS {automatic}
> 2 2 2 0 0 0
> 
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