The ABINIT Users Mailing List ( CLOSED )

[Mitrokhin <mit@uni.udm.ru>]

On Fri, 7 Mar 2008 10:26:58 +0100
mingyang@nus.edu.sg wrote:

> 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

Dear Yang Ming,

I also use VASP and ABINIT for the calculation of lattice constant.
ABINIT gives good results if you use PAW with GGA (PBE, RPBE, BLYP, ...).
But it is more timeconsuming with compare to VASP. The LDA gives the
underestimate value, the 10-15% less to the experiment and GGA calculations.

Best regards,

Yuri
 
--------------------------------------------------------------
Yuri Mitrokhin, Ph.D.                   Phone:  +7 3412 916089
Department of Mathematics               Fax:    +7 3412 755866  
Udmurt State University                 http://www.udsu.ru      
1 Universitetskaia St.                  E-mail: mit@uni.udm.ru  
426034 Izhevsk  RUSSIA          
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