[Pw_forum] Na phonon issues
Miguel Martínez Canales
wmbmacam at lg.ehu.es
Thu May 17 16:30:25 CEST 2007
Dear folks,
I've been doing some phonon calculations on Na lately, and I've got an
issue with the Na.pw91-n-mt.UPF pseudopotential. Well, it might be an issue
with the input, so I also attach them.
When doing a phonon calculation at q=(0 -0.1 0.1) for bcc Na, which is the
same as na.dyn2 in the enclosed input, I get the following frequencies:
$ tail na.dyn2
q = ( 0.000000000 -0.100000000 0.100000000 )
**************************************************************************
omega( 1) = -0.102259 [THz] = -3.411026 [cm-1]
( 0.000000 0.000000 -0.707107 0.000000 -0.707107 0.000000 )
omega( 2) = 0.766410 [THz] = 25.564857 [cm-1]
( 1.000000 0.000000 0.000000 0.000000 0.000000 0.000000 )
omega( 3) = 1.171147 [THz] = 39.065511 [cm-1]
( 0.000000 0.000000 -0.707107 0.000000 0.707107 0.000000 )
**************************************************************************
If I use the LDA pseudo Na.pz-n-vbc.UPF near equilibrium (a=7.738a_0) with
ecut=30 Ry and 18 18 18 shifted M-P grid, I get the following omegas:
omega( 1) = 0.273215 [THz] = 9.113532 [cm-1]
omega( 2) = 0.835358 [THz] = 27.864728 [cm-1]
omega( 3) = 1.264994 [THz] = 42.195940 [cm-1]
While the Na.pbe-sp-van_ak.UPF pseudo, with the same grid as the enclosed
input (20 20 20 shifted M-P), ecut=35 and ecutrho=300 Ry, I get also
sensible results (with 7.932 a_0 as lattice parametre):
omega( 1) = 0.390200 [THz] = 13.015753 [cm-1]
omega( 2) = 0.857166 [THz] = 28.592182 [cm-1]
omega( 3) = 1.238921 [THz] = 41.326237 [cm-1]
So I have the following question: Is the mechanical instability I see a
product of my input or a product of the pseudopotential?
Thanks a lot,
Miguel
============= input follows ==============
# self-consistent run
cat > na.scf.in << EOF
&control
calculation='scf'
restart_mode='from_scratch',
tstress = .true.
tprnfor = .true.
prefix='na',
pseudo_dir = '$PSEUDO_DIR/',
outdir='$TMP_DIR/'
/
&system
ibrav= 3, celldm(1) = 7.8956 , nat= 1, ntyp= 1,
ecutwfc = 35.0,
occupations='smearing', smearing='m-p', degauss= 0.010
/
&electrons
conv_thr = 1.0d-8
mixing_beta = 0.7
/
ATOMIC_SPECIES
Na 22.989768 Na.pw91-n-mt.UPF
ATOMIC_POSITIONS
Na 0.00 0.00 0.00
K_POINTS {automatic}
20 20 20 1 1 1
EOF
# phonon calculation
cat > na.ph.in << EOF
phonons of Na
&inputph
tr2_ph=1.0d-16,
prefix='na',
ldisp=.true.,
nq1=10, nq2=10, nq3=10
amass(1)=22.989768,
outdir='$TMP_DIR/',
fildyn='na.dyn',
/
EOF
--
----------------------------------------
Miguel Martínez Canales
Dto. Física de la Materia Condensada
UPV/EHU
Facultad de Ciencia y Tecnología
Apdo. 644
48080 Bilbao (Spain)
Fax: +34 94 601 3500
Tlf: +34 94 601 5437
----------------------------------------
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