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["zeng zhenhua" <myid520@hotmail.com>]

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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