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[zfhou@mail.edu.cn]

Dear Dr. Hamann,

Thanks very much!

According to your suggestion and the exmaples in Test_v4, I have calculated 
the elastic constant of Si again by abinis and anaddb.

The C11, and C12 that I got is  160.77 GPa and 63.12 GPa,respectively, which 
are very close the experiment value 166.0 GPa and 64 GPa [1], respectively. 
But The C44 is 108.4GPa and is larger than the experiment value 79.6GPa [1].

The warning comments from the outputs tell me that I should increase the 
cutoff and k mesh.  But I think that the ecutoff and k-points sampling I used 
is sufficient for this calculation.  So I think the reason is from other 
parameters in my input file.
But until now I haven't found out the real reason.

The folloing is the warning in my output file.

"phonon modes warning- :
accoustic sum rule violation met:the eigenvalues of accoustic mode
are too large at Gamma point
increase cutoff energy or k-points sampling."


I used the HGH pseudopotential, CA-LDA (ixc =2 ), the lattice constant of 
10.1738 a.u.(in experiment, a0=10.261 a.u. for Si) which is optimized and 
fitted by EOS, Ecut of 12 Ha, k mesh of 8 x 8 x 8 corresponding to 60 k 
points in IBZ.

By EOS, I got the bulk modulus of silicon (diamond strucutre) is 95.497 GPa, 
which is very close to the experimental value of 98 GPa (B = (C11+2C12)/3.0) 
for cubic crystals). 

[1]. A. Darys and J. Kundrotas "handbook on physical properties Ge, Si, GaAs  
and InP" (Vilnius: Science and Encyclopedia Publisher)

Regards
zhufeng

---------the input for abinis--------
ndtset 3 
# Set 1 : initial self-consistency
kptopt1   1
tolvrs1 1.0d-18
iscf1 5

#set 2 the ddk 
rfelfd2 2  # only derivative of the gs wf
rfdir2 1 1 1
nqpt2 1
qpt2 0.0 0.0 0.0 #only the gamma point
getwfk2 -1
kptopt2 2
iscf2 -3
tolwfr2 1.0d-20

# Set 3 : response-function strain calculation
rfphon3 1
rfatpol3 1 2  
rfelfd3 3
rfdir3 1 1 1
nqpt3 1
qpt3 0 0 0
rfstrs3  3
getwfk3 -2
getddk3 -1
kptopt3 2
tolvrs3 1.0d-16
iscf3 5

#comon input data
 diemac   12.0
   ecut   12.0
   ixc 2
   iscf   5
  nband   12
  ngkpt   8  8  8
 nloalg   4
  nstep   24
 prtvol   10
nshiftk 4                       
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
acell 3*10.1738
rprim  0.0  0.5  0.5    
       0.5  0.0  0.5    
       0.5  0.5  0.0   
ntypat   1 
typat   2*1
natom   2
xred           
   0.0  0.0  0.0       
   0.25 0.25 0.25     
znucl 14 
--------------------END----------------------
------------Input for anaddb----------
# General informations
#**********************
   rfmeth  1
   enunit  0
   eivec   1
   asr     1
   chneut  2
   slectz  0

# Flags
#*******
   dieflag  2
   ifcflag  0
   thmflag  0
elaflag  3 

polflag 1
relaxat 1
relaxstr 1
nstrfix 2
istrfix 1 2
targetpol 0.0 0.0 0.45

# Frequence information
#***********************
   nfreq   100
   frmin   0 
   frmax   2E-3

# Interatomic force constant information
#****************************************
   dipdip  1
   nspher  0
   ifcout  0
   ifcana  0
   natifc  2
   atifc   1 2

# Thermal information  (needed if thmflg is 1)
#**********************************************
   nchan       500
   nwchan      10
   dostol      0.1 
   thmtol      0.05
   ntemper     300
   tempermin   10.0
   temperinc   1.0

# Wavevector grid number 1
#**************************
   brav  1
   ngqpt 4 4 4
   nqshft 1
   q1shft 0 0 0

# Wavevector grid number 2
#**************************
   ngrids 12 
   ng2qpt 24 24 24

# Wavevector list number 1 
#**************************
   nph1l 1
   qph1l 0 0 0 1

# Wavevector list number 2 (Gamma point only, with limiting direction
#           in cartesian coordinates. )
#*********************************************************************
   nph2l 3
   qph2l 1.0  0.0  0.0  0
         0.0  1.0  0.0  0
         0.0  0.0  1.0  0 
--------END-----------------------------------