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

Dear Xavier Gonze,
Thank you for your help. I think your suggestions are ingenious.
The reason I want to fix the bottom three layers is that I want to make 
these  layers like bulk layres to the top three layers.Then the top three 
layeres exhibit characteristics of a real surface layers. But if I have 
full  relaxation ,the top thre layers will lose real surface layers 
condition. So i have one surface relaxation. Is there has other methods? 
your suggestion will be greatly appreciated!
Thank you again!
Best regards.

Zhenhua Zeng
Hunan University ,PR. china


> From: Xavier Gonze <gonze@pcpm.ucl.ac.be>
> Reply-To: forum@abinit.org
> To: forum@abinit.org
> Subject: Re: [abinit-forum] fixsym problem
> Date: Tue, 28 Sep 2004 10:10:39 +0200
>
> 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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> >
> >

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