The ABINIT Users Mailing List ( CLOSED )

[Scott Beckman <spbeckman@gmail.com>]

The number of k-points is probably OK, but in my experience an ecut  
of around 20 Hartree is needed.

It is worth noting that the Ge pseudopotential is a bit odd.  The all- 
electron LDA calculation returns a band gap of 0 eV, but the  
pseudopotentials don't.  If you take a pseudopotential generator and  
create a dozen or so potentials and test them you'll find differences  
in the band structure.  However, the structural and mechanical  
properties seem pretty constant and match experiment well.  If you're  
going to work with Ge, it might be worth looking at:  Tiago et al.  
PRB V69 P125212 (2004).

Scott

On Mar 7, 2008, at 5:04 AM, Aldo Humberto Romero wrote:

> Dear Yang
>
> your cutoff energy is way to low... 12Ry for a TM pseudo
> is really low (even in Vasp, which are are soft pseudos,
> the cutoff is higher)... you should check energy convergence
> as function of cutoff and then look at acell.
>
> By the way, I have not experience with Ge,
> but you can also play with the number
> of Kpoints after you energy convergence study.
>
> regards
>
> -aldo.
>
> > Dear All,
> >
> > I optimized the lattice constant of Ge following the ABINIT  
> > tutorial. The
> > value I got is about 5.52Angstrom, which is not in good agreement  
> > with the
> > experimental value (5.66Angstrom), the gap about 2%. I did the  
> > similar
> > calculation using VASP, and the error is within 0.5%, so I think the
> > lattice constant of Ge I got by ABINIT is not nice, but I don?t  
> > know where
> > I lost. Can any one there help me to correct my input files or  
> > give me
> > some suggestions? The pseudopotential I use is Troullier-Martins LDA
> > pseudopotential, and the input file is like following.
> >
> > _____________________________
> >
> > # optimize the lattice constat
> >
> > optcell 1
> >
> > ionmov  3
> >
> > ntime  10
> >
> > dilatmx 1.1
> >
> > ecutsm  0.5
> >
> > #Definition of the unit cell
> >
> > acell 3*10.699         # This is equivalent to   10.62 10.62 10.62
> >
> > rprim  0.0  0.5  0.5   # In lessons 1 and 2, these primitive vectors
> >
> >        0.5  0.0  0.5   # (to be scaled by acell) were 1 0 0  0 1  
> > 0  0 0 1
> >
> >        0.5  0.5  0.0   # that is, the default.
> >
> >
> >
> > #Definition of the atom types
> >
> > ntypat 1          # There is only one type of atom
> >
> > znucl 32         # 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  
> > Ge.
> >
> > #Definition of the atoms
> >
> > natom 2           # There are two atoms
> >
> > typat 1 1         # They both are of type 1, that is, Ge
> >
> > xred              # This keyword indicate that the location of the  
> > atoms
> >
> >                   # will follow, one triplet of number for each atom
> >
> >    0.0  0.0  0.0  # Triplet giving the REDUCED coordinate of atom 1.
> >
> >    1/4  1/4  1/4  # Triplet giving the REDUCED coordinate of atom 2.
> >
> >                   # Note the use of fractions (remember the limited
> >
> >                   # interpreter capabilities of ABINIT)
> >
> > #Definition of the planewave basis set
> >
> > ecut 12.0 # Maximal kinetic energy cut-off, in Hartree
> >
> > #Definition of the k-point grid
> >
> > kptopt 1          # Option for the automatic generation of k points,
> > taking
> >
> >                   # into account the symmetry
> >
> > ngkpt  6 6 6      # This is a 6x6x6 grid based on the primitive  
> > vectors
> >
> >
> >
> > nshiftk 4         # of the reciprocal space (that form a BCC  
> > lattice !),
> >
> >                   # repeated four times, with different shifts :
> >
> > shiftk 0.5 0.5 0.5
> >
> >       0.5 0.0 0.0
> >
> >       0.0 0.5 0.0
> >
> >       0.0 0.0 0.5
> >
> > #Definition of the SCF procedure
> >
> > nstep 60         # Maximal number of SCF cycles
> >
> > toldfe 1.0d-6     # Will stop when, twice in a row, the difference
> >
> >                   # between two consecutive evaluations of total  
> > energy
> >
> >                   # differ by less than toldfe (in Hartree)
> >
> > diemac 12.0
> >
> > Thanks.
> >
> >
> >
> > Best regards,
> >
> > Yang Ming
> >
> >
> >
> > ******
> >
> > Computational Condensed Matter Physics
> >
> > Department of Physics
> >
> > National University of Singapore
> >
> > Singapore, 117542
> >
> > Tel: (65) 65164335 (office)
> >
> > Email: mingyang@nus.edu.sg
>
>
> --
> Dr. Aldo Humberto Romero
> FULL PROFESSOR CINVESTAV - Unidad Queretaro
> Libramiento Norponiente 2000
> Real de Juriquilla, CP 76230, Qro, Queretaro
> Mexico
>
> Phone: + 52 442 441 4909
> NEW PHONE (FROM MARCH 13): +52 (442) 211 9909
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> Email: aromero@qro.cinvestav.mx
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