Constraining local magnetic moments

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Task

Constraining the local magnetic moments on an Fe dimer.

Input

POSCAR

Fe dimer                               
 1.00000000000000000
     8.0000000000000000    0.0000000000000000    0.0000000000000000
     0.0000000000000000    8.0000000000000000    0.0000000000000000
     0.0000000000000000    0.0000000000000000    8.0000000000000000
   2
Cartesian
 3.00  0.00  0.00
 5.00  0.00  0.00

INCAR

SYSTEM        = Fe dimer
ISTART        = 0
ISYM          = 0
LNONCOLLINEAR = .TRUE.
MAGMOM        = 0 0 3   0 0 3
VOSKOWN       = 1
LORBIT        = 11
  
! mix slowly when increasing LAMBDA 
# AMIX          = 0.1
# BMIX          = 0.00001
# AMIX_MAG      = 0.2
# BMIX_MAG      = 0.00001
  
# I_CONSTRAINED_M = 1
# RWIGS           = 1.0
# LAMBDA         = 10
# M_CONSTR        = 0 0 1  0 0 1

• Symmetry is switched off (ISYM=0).
• Initially moments for ferromagnetic calculation are initialized.

KPOINTS

k-points
0
Monkhorst Pack
  1   1   1
  0.  0.  0.

• A single k point in the calculation is sufficient.

Calculation

• By using the initial ferromagnetic initialization of MAGMOM = 0 0 3 0 0 3 we get the following magnetic moments in the OSZICAR file:

...
DAV:  20    -0.929676054634E+01   -0.26101E-03   -0.16780E-03    60   0.102E-01    0.537E-02
DAV:  21    -0.929679955346E+01   -0.39007E-04   -0.30319E-04    60   0.590E-02
   1 F= -.92967996E+01 E0= -.93047629E+01  d E =0.238900E-01  mag= -0.0006 -0.0003  6.0537

• By using a different initial magnetization of MAGMOM = 0 0 3 0 2 2 the system converges to a ferromagnetic solution:

 magnetization (y)                          magnetization (z)
# of ion     s       p       d       tot   # of ion     s       p       d       tot
----------------------------------------   ----------------------------------------
  1        0.018  -0.001   1.071   1.087     1        0.045  -0.003   2.587   2.628
  2        0.019  -0.001   1.069   1.087     2        0.045  -0.003   2.588   2.629
----------------------------------------   ----------------------------------------
tot        0.037  -0.003   2.140   2.174   tot        0.089  -0.007   5.175   5.257

• A penalty functional is added to the system, driving the integrated local moments into the desired directions, when the following steps are modified in the input (beware the penalty functional contributes to the total energy):
  • Switching on constraints on magnetic moments (I_CONSTRAINED_M=1).
  • Setting integration radius to determine local moments (RWIGS=1.0).
  • Weight in penalty functional (LAMBDA=10).
  • Target directions for constraints on magnetic moments (M_CONSTR= 0 0 1 0 1 1).

Download

4_5_Fe_dimer.tgz

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