[Pw_forum] problem with vc-relax and spin-polarization

[Bryan M. Wong]

Hi,

     I seem to have a problem doing "vc-relax" with the
"starting_magnetization" initialization turned on.

     I can always do a regular "relax" with the starting_magnetization
guess, and the structure will relax with a magnetic state constrained to my
*fixed* unit cell dimensions. However, when I do a *vc-relax* with
starting_magnetization set to any non-zero value, the 2nd step in the cell
relaxation always reverts to the spin-unpolarized case (and the optimization
will continue with the spin-unpolarized case).

     I have attached an example of this behavior for a simple graphene
nanoribbon.  After the first step, the nanoribbon is magnetic and nonzero,
but the 2nd step reverts back to a non-magnetic initial condition.

     Is there any way around this (without constraining the magnetization to
a fixed value for all steps)?

Thanks,
Bryan



&CONTROL
                 calculation = 'vc-relax' ,
               etot_conv_thr = 1.0e-4 ,
               forc_conv_thr = 1.0e-3 ,
                     tstress = .true. ,
                     tprnfor = .true. ,
 /
 &SYSTEM
                       ibrav = 8,
                   celldm(1) = 4.644592221,
                   celldm(2) = 6.70720764,
                   celldm(3) = 4.393200375,
                         nat = 10,
                        ntyp = 4,
                     ecutwfc = 60.D0 ,
                       nosym = .false. ,
                        nbnd = 28,
                       nelec = 34,
                  tot_charge = 0.000000,
                 occupations = 'smearing' ,
                     degauss = 0.02 ,
                    smearing = 'gaussian' ,
                       nspin = 2 ,
   starting_magnetization(1) = 1.0,
   starting_magnetization(2) = -1.0,
   starting_magnetization(3) = 1.0,
   starting_magnetization(4) = -1.0,
 /
 &ELECTRONS
                    conv_thr = 1.D-6 ,
                 mixing_beta = 0.7D0 ,
 /
 &IONS
                ion_dynamics = 'bfgs' ,
           pot_extrapolation = 'second_order' ,
           wfc_extrapolation = 'second_order' ,
            trust_radius_ini = 0.2D0 ,
 /
ATOMIC_SPECIES
   H1    1.00000  H.pbe-rrkjus.UPF
   C1   12.00000  C.pbe-rrkjus.UPF
   C2   12.00000  C.pbe-rrkjus.UPF
   H2    1.00000  H.pbe-rrkjus.UPF
ATOMIC_POSITIONS crystal
   H1      0.000000000    0.218692155    0.000000000    1  1  0
   C1      0.000000000    0.284883518    0.000000000    1  1  0
   C2      0.500000000    0.326062773    0.000000000    1  1  0
   C1      0.500000000    0.413734370    0.000000000    1  1  0
   C2      0.000000000    0.456468822    0.000000000    1  1  0
   C1      0.000000000    0.543530576    0.000000000    1  1  0
   C2      0.500000000    0.586265119    0.000000000    1  1  0
   C1      0.500000000    0.673937250    0.000000000    1  1  0
   C2      0.000000000    0.715116935    0.000000000    1  1  0
   H2      0.000000000    0.781308481    0.000000000    1  1  0
K_POINTS automatic
  13 1 1   0 0 0
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20100621/2c9bdac6/attachment.html>