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[mingyang@nus.edu.sg]

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