The ABINIT Users Mailing List ( CLOSED )

[Xavier Gonze <gonze@pcpm.ucl.ac.be>]

Dear Zeng Zhenhua,

I think you gain nothing in trying to fix the three lowest layers.
You might simply relax all atoms, and keep the initial symmetry.

However, if you still want to fix the three lowest layers,
and perform a unconstrained relaxation of the other atoms,
give all the non-fixed atoms a slight random displacement :
The symmetry analyzer will not find any symmetry, and the
fixsym routine will not complain anymore.

Best wishes,
Xavier Gonze


zeng zhenhua wrote:
> Hello everyone:
>    happy mid-autumn festival!
>    I am calculating  110 surface of slab Aurum. The supercell being used 
> is made up of six layers of Au atoms with the bottom three layers being 
> fixed. The surpercell also include an vacuum layer correspons to six 
> layers of Au atoms.  But the Log files give the following error:
> 
> fixsym: ERROR -
>  Atom number      6 is symmetrically equivalent to atom number      1,
>  but according to iatfix, iatfixx, iatfixy and iatfixz, they
>  are not fixed along the same directions, which is forbidden.
>  Action : modify either the symmetry or iatfix(x,y,z) and resubmit.
> 
>   Does it mean the nsym and symrel must be set by hand? I think setting 
> nsym and symrel by hand is very difficult to me.So I don't kown how to 
> do. Could anyone give me some ideas?
> your help will be greatly appreciated!
> Thanks a lot.
> Best regards.
> 
> Zhenhua Zeng
> Hunan University ,PR. china
> 
> ###########################################################
> input file
> 
> # Crystalline  Aurum # 6 Aurum layers,6 vacuum layers.
> # The botton 3 Aurum layers are fixed
> 
> iscf 3
> nline 5
> iprcel  45
> 
> occopt 4
> tsmear 0.01
> 
> #Definition of the k-point grids
> kptopt 1          # Option for the automatic generation of k points, taking
>                  # into account the symmetry
> nshiftk  2              #for slab shiftk 0.5 0.0 0.0       #for slab
>       0.0 0.5 0.0 
> #Definition of the unit cell
> acell 7.9916 2*5.650914   #110 surface of Aurum                          
> #fcc Autum lattice constant is 4.08 Angstrom ,equal to 7.710 Bohr
> rprim  1.0 0.0 0.0
>       0.0 1.0 0.0
>       0.0 0.0 6.0   #  FCC  Aurum,110 surface,6 vacuum layers
> chkprim 0
> 
> ngkpt  4 6 1
> 
> #Optimization of the lattice parameters
> ionmov  3
> ntime  100
> ecutsm  0.5
> tolmxf 5.0d-4
> 
> #Definition of the atom types
> ntypat 1          # There is only one type of atom
> znucl 79         # The keyword "znucl" refers to the atomic number of 
> the                  # possible type(s) of atom. The pseudopotential(s) 
>                  # mentioned in the "files" file must correspond
>                  # to the type(s) of atom. Here, the only type is Aurum
>                        
> #Definition of the atoms
> natom 6           # There is only one atom per cell
> typat   20*1     # This atom is of type 1, that is, Aluminum.
> 
> natfix 3         # The botton 3 Aurum layers are fixed
> iatfix  1 2 3
> 
> xred    0.0000000000E+00  0.0000000000E+00  0.0000000000E+00
>        5.0000000000E-01  5.0000000000E-01  8.3333333333E-02
>        0.0000000000E+00  0.0000000000E+00  1.6666666667E-01
>        5.0000000000E-01  5.0000000000E-01  2.5000000000E-01
>        0.0000000000E+00  0.0000000000E+00  3.3333333333E-01
>        5.0000000000E-01  5.0000000000E-01  4.1666666667E-01
> 
> #corresponding Cartesian coordinates
> #xcart
>    3*0.0                        #the first layer,    3.9958  2.825457  
> 2.825457   #the second layer,
>    0.0    0.0        5.650914   #the third layer,
>    3.9958  2.825457  8.476371   #the forth layer,
>    0.0    0.0        11.301828   #the fifth layer
>    3.9958  2.825457  14.127285   #the sixth layer,   
> #Exchange-correlation functional
> ixc 11             # GGA
> 
> #Definition of the planewave basis set
> ecut 20           # Maximal kinetic energy cut-off, in Hartree
> 
> #Definition of the SCF procedure
> nstep 100          # Maximal number of SCF cycles
> toldfe 1.0d-6
> 
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