Dear all:
The example2 is about the phonon mode computation of Gamma and X points
for the silicon. In the example, the k-points
were set as:
K_POINTS
10
0.1250000 0.1250000 0.1250000 1.00
0.1250000 0.1250000 0.3750000 3.00
0.1250000 0.1250000 0.6250000 3.00
0.1250000 0.1250000 0.8750000 3.00
0.1250000 0.3750000 0.3750000 3.00
0.1250000 0.3750000 0.6250000 6.00
0.1250000 0.3750000 0.8750000 6.00
0.1250000 0.6250000 0.6250000 3.00
0.3750000 0.3750000 0.3750000 1.00
0.3750000 0.3750000 0.6250000 3.00
-----------------------------------------------------
the results are reasonable agree with the experimental results. But when I use
those K-points for the K(0.75,0.75,0) and L(0.5,0.5,0.5) points, the results
are not good (L(TA)) which are listed in the 2nd column of the table .
I also use k-points automatic generated with :
K_POINTS automatic
8 8 8 1 1 1
the wavelengths of the phonon modes for the four points (listed in the 3rd
column of the table)are all different from the experimental results, especially
for the low frequency modes, such as the X(TA) and L(TA).
***********************************************************************************************
------------------------------------------------------------------------------------------
experimental(cm-1) special points automatic generation
computational(cm-1) computational(cm-1)
Gamma(TO) 517 510 501
Gamma(LO) 517 510 501
X(TA) 150 140 212
X(LA) 410 408 427
X(TO) 463 458 468
X(LO) 410 408 427
L(TA) 114 190 190
L(LA) 378 402 398
L(TO) 487 509 498
L(LO) 417 437 424
---------------------------------------------------------------------------------------
************************************************************************************************
the experimental result get from the paper: P.R.B. 43, 7231 Paolo
Giannozzi,Stefano de Gironcoli, Pasquale Pavone and Stefano Baroni
the pw input file for the X point with k-poins generated automatically is shown
as follows:
&control
calculation='phonon'
prefix = 'Si-X'
pseudo_dir = '/home/wien2k/pw/pseudo/',
outdir='/biology/wien2k/pwwork/Si/v0/X/'
/
&system
ibrav= 2, celldm(1) =10.263107, nat= 2, ntyp= 1,
ecutwfc =18.0,
/
&electrons
conv_thr = 1.0d-8
/
&phonon
xqq(1)=1.0, xqq(2)=0.0, xqq(3)=0.0
/
ATOMIC_SPECIES
Si 28.086 Si.vbc.UPF
ATOMIC_POSITIONS
Si 0.00 0.00 0.00
Si 0.25 0.25 0.25
K_POINTS automatic
8 8 8 1 1 1
-----------------------------------------
while the ph files for the X point is shown as follows :
&inputph
tr2_ph=1.0d-14,
prefix='Si-X',
amass(1)=28.08,
outdir='/biology/wien2k/pwwork/Si/v0/X/',
fildyn='Si-X.dynX',
/
1.0 0.0 0.0
------------------------------------------------------
Why the k-points generated with automatic mode could not get the right
results, or Is there something wrong in my input files? Is there deeply
difference between the two ways of setting k-points? Must I produce different
k-points for different points in reciprocal space by hand, and how to do that
for the K and L points?
Any direction,comments or examples are appreciated!
Best Regards!
S. R. Sun
---------------------------------------------
Beijing Synchrotron Radiation Facility
Institute of High Energy Physics
Chinese Academy of Sciences
P. O. Box 918, 100049 Beijing
P. R. China
Tel: 0086+10 88236710
email:sunsr at ihep.ac.cn
