[Pw_forum] vc-relax

[Cao TF]

Dear QE users:
   I want to do the 'vc-relax'  calculation of bilayer structure of graphene and BN.  And  only  the lattice constant  a, b are allowed to change in the relaxation. So I set  cell_dofree  = 'xy' ,  but when the calculation finished,  the  distance of of the vacuum between different  by layers also changed.  The vacuum  is set 10 A, it changed to 5.76 A in the end.   What can be the reasons ?  Any suggestions will be greatly appreciated.
 cell_dofree 	CHARACTER
Default: 	'all'

    Select which of the cell parameters should be moved:

    all     = all axis and angles are moved
    x       = only the x axis is moved
    y       = only the y axis is moved
    z       = only the z axis is moved
    xy      = only the x and y axis are moved, angles are unchanged
    xz      = only the x and z axis are moved, angles are unchanged
    yz      = only the y and z axis are moved, angles are unchanged
    xyz     = x, y and z axis are moved, angles are unchanged
    shape   = all axis and angles, keeping the volume fixed




Research Laboratory for Computational Materials Sciences, Institute of Solid State Physics,
Chinese Academy of Sciences 





              

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