[Pw_forum] **some confusion about spin related knobs**

[吴 华华]

Hi,every pwscf experts and users in this community .

It has been almost one year since I abandoned VASP. In the past one year , 
I learned much from the community of pwscf, which is a free world full of 
many gifted men.



I am reproducing the published study of the high spin (HS)/low spin (LS) 
transition in low solute concentration magnesiowustite (Mw), 
(Mg(1-x)Fe(x))O, (x < 20%), by Tsuchiya T etc.

Under the guide of  INPUT_PW file ,I know some knobs that control spin 
related calculation,such as  nspin , 
starting_magnetization(i),tot_magnetization etc.

In order to contain the Fe with the desired proportion,supercell is needed.
I did not use the primitive fcc cell,for it reduces the number of Fe x 
proportion, instead a conventional cubic supercell is used,as you can see 
in my input file below.
You know, when there is only one Fe in the supercell ,things come much 
easy.
But 5 Fe atoms is another story.




Let's hit the point.

1.the main puzzle is that 
 I can only controll the tot_magnetization of all the atoms in the 
supercell ,but not the respective Fe ， which  prevents  me assembling HS 
and LS Fe atoms.
 starting_magnetization(i)  seems to have the capacity to control each Fe， 
but from the literal meaning, it seems to only give a initial status , and 
from my testing calculation it does evolve with the relax calculation.

2.another minor puzzle is that
How to spread the Fe atoms in the supercell,which satisfied the following 
requirement:
give the Fe atoms as mamy symmetries as possible
keep th Fe atoms as far as possible to avoid the 3d electrons interactions
I have write several possible assemblings with the help of XCrySDen and my 
own eyes! But I do not satisfied with them.   is there any routines or 
special techniques to handle them?


I will be much appreciated, if  my confusion  could be cleared .

input file for  HS 
///////////////////////////////////////
&CONTROL
                 calculation = 'relax' ,
                restart_mode = 'from_scratch' ,
                      outdir = './tmp/' ,
                  pseudo_dir = '/home/wu/mpich2/espresso-3.2/pseudo/MgFeO/' 
,
                      prefix = 'MgFeO_super_cubic' ,
                     tstress = .TRUE. ,
                     tprnfor = .TRUE.,
                    etot_conv_thr=1.0d-6,  forc_conv_thr=1.0D-4 
                      
 /
 &SYSTEM
                       ibrav = 0,
                         nat = 64,
                        ntyp = 6,
                      ecutwfc = 30 ,
                     ecutrho  = 144,
                     nbnd = 400,
                     nspin = 2, 
       starting_magnetization(3) = 1.0 
       angle1(3) = 90.0
       angle2(3) =  0.0 
       starting_magnetization(4) = 1.0
       angle1(4) = 90.0
       angle2(4) =  0.0 
       starting_magnetization(5) = 1.0
       angle1(5) = 90.0
       angle2(5) =  0.0    
       starting_magnetization(6) = 1.0 
       angle1(6) = 90.0
       angle2(6) =  0.0     
       tot_magnetization = 16          
       lda_plus_u=.true.  Hubbard_U(3)=5.0, Hubbard_U(4)=5.0,
                          Hubbard_U(5)=5.0 ,  Hubbard_U(6)=5.0
                   
 /
 &ELECTRONS
                    conv_thr = 1.0d-6 ,
                 mixing_mode = 'plain' ,
                 mixing_beta = 0.7 ,   
/
&IONS
  ion_dynamics = 'bfgs',
  pot_extrapolation =  "second_order",
  wfc_extrapolation = "second_order",
/
CELL_PARAMETERS cubic
16.2  0.0  0.0
 0.0 16.2  0.0
 0.0  0.0 16.2
ATOMIC_SPECIES
   Mg   24.30500  Mg.pw91-np-van.UPF 
    O   15.99940  O.pw91-van_ak.UPF
   Fe1    55.8452  Fe.pw91-sp-van_ak.UPF
   Fe2    55.8452  Fe.pw91-sp-van_ak.UPF
   Fe3    55.8452  Fe.pw91-sp-van_ak.UPF
   Fe4    55.8452  Fe.pw91-sp-van_ak.UPF
ATOMIC_POSITIONS {crystal}
Mg 0.00000 0.00000 0.00000
Fe1 0.00000 0.00000 0.50000
Fe2 0.00000 0.50000 0.00000
Mg 0.00000 0.50000 0.50000
Fe3 0.50000 0.00000 0.00000
Mg 0.50000 0.00000 0.50000
Mg 0.50000 0.50000 0.00000
Fe4 0.50000 0.50000 0.50000   
Mg 0.00000 0.25000 0.25000
Mg 0.00000 0.25000 0.75000
Mg 0.00000 0.75000 0.25000
Mg 0.00000 0.75000 0.75000
Mg 0.50000 0.25000 0.25000
Mg 0.50000 0.25000 0.75000
Mg 0.50000 0.75000 0.25000
Mg 0.50000 0.75000 0.75000
Mg 0.25000 0.00000 0.25000
Mg 0.25000 0.00000 0.75000
Mg 0.25000 0.50000 0.25000
Mg 0.25000 0.50000 0.75000
Mg 0.75000 0.00000 0.25000
Mg 0.75000 0.00000 0.75000
Mg 0.75000 0.50000 0.25000
Mg 0.75000 0.50000 0.75000
Mg 0.25000 0.25000 0.00000
Mg 0.25000 0.25000 0.50000
Mg 0.25000 0.75000 0.00000
Mg 0.25000 0.75000 0.50000
Mg 0.75000 0.25000 0.00000
Mg 0.75000 0.25000 0.50000
Mg 0.75000 0.75000 0.00000
Mg 0.75000 0.75000 0.50000
O 0.25000 0.25000 0.25000
O 0.25000 0.25000 0.75000
O 0.25000 0.75000 0.25000
O 0.25000 0.75000 0.75000
O 0.75000 0.25000 0.25000
O 0.75000 0.25000 0.75000
O 0.75000 0.75000 0.25000
O 0.75000 0.75000 0.75000
O 0.25000 0.00000 0.00000
O 0.25000 0.00000 0.50000
O 0.25000 0.50000 0.00000
O 0.25000 0.50000 0.50000
O 0.75000 0.00000 0.00000
O 0.75000 0.00000 0.50000
O 0.75000 0.50000 0.00000
O 0.75000 0.50000 0.50000
O 0.00000 0.25000 0.00000
O 0.00000 0.25000 0.50000
O 0.00000 0.75000 0.00000
O 0.00000 0.75000 0.50000
O 0.50000 0.25000 0.00000
O 0.50000 0.25000 0.50000
O 0.50000 0.75000 0.00000
O 0.50000 0.75000 0.50000
O 0.00000 0.00000 0.25000
O 0.00000 0.00000 0.75000
O 0.00000 0.50000 0.25000
O 0.00000 0.50000 0.75000
O 0.50000 0.00000 0.25000
O 0.50000 0.00000 0.75000
O 0.50000 0.50000 0.25000
O 0.50000 0.50000 0.75000
K_POINTS automatic
5 5 5 0 0 0 
/////////////////////////////////////////////////////////





***********************************************
Wu Changhua , 
Institute of Geology and Geophysics, 
CAS , POB.9825  Beijing 100029  China

Email:  changhuacas at hotmail.com

***********************************************

_________________________________________________________________
免费下载 MSN Explorer:   http://explorer.msn.com/lccn