[Pw_forum] phonon calc. for fcc at X
e kb
eminekb at yahoo.com
Sun Dec 10 17:57:14 CET 2006
Dear Stefano , QE users,
Thank you for your interest,
Here are the scf, nscf and ph.x input files respectively, for X(0,0,1).
For X(0,1,1) the scf file is the same, in nscf input I just changed the phonon namelist to (0.00 1.00 1.00) so not to make the mail longer and unreadable, I am skipping it and just adding ph.X input for X(0,1,1).
I should note that this was a part of test calculations for the new pseudo for Indium that I recently generated using the 'atomic' code. The cut off energy that I used for these calculations (34 Ryd) is chosen to be enough to represent correct lattice constants, but still the pseudo and the value of cut off energy needs further examination. That is why I would not be surprised to see any discrepiencies in the frequencies. But again, I could not understand the differences that occured for the same point.
With a verbose output I checked the phonon polarization vectors,
As far as I understand, the calculation is done for the same modes for the two points.
I do not want to bother you with the whole output files,
if this is a very simple problem that an experienced/careful user can notice from the inputs,
otherwise I can attach the output files.
Buona domenica,
Emine Kucukbenli
------------
&control
calculation = 'scf'
restart_mode='from_scratch',
prefix='34_vib',
tprnfor = .true.
pseudo_dir = '$PSEUDO_DIR' ,
etot_conv_thr = 1.0D-5
/
&system
ibrav= 2,
celldm(1)=9.593140000
nat= 2,
ntyp= 2,
ecutwfc =34.0,
ecutrho =272.0,
occupations = 'smearing'
smearing = 'gaussian'
degauss = 0.004,
/
&electrons
mixing_mode = 'plain'
mixing_beta = 0.7
/
ATOMIC_SPECIES
In 114.818 In_us_2.upf
N 14.0067 N.pbe-van_ak.UPF
ATOMIC_POSITIONS { crystal }
In 0.00000000000 0.00000000000 0.0000000000000
N 0.25000000000 0.25000000000 0.2500000000000
K_POINTS { automatic }
8 8 8 0 0 0
------------
&control
calculation = 'phonon'
restart_mode='from_scratch',
prefix='34_vib',
tprnfor = .true.
pseudo_dir = '$PSEUDO_DIR' ,
etot_conv_thr = 1.0D-5
/
&system
ibrav= 2,
celldm(1)=9.593140000
nat= 2,
ntyp= 2,
ecutwfc =34.0,
ecutrho =272.0,
occupations = 'smearing'
smearing = 'gaussian'
degauss = 0.004,
/
&electrons
mixing_mode = 'plain'
mixing_beta = 0.7
/
&phonon
xqq(1) = .00, xqq(2) = .00, xqq(3) = 1.00
/
ATOMIC_SPECIES
In 114.818 In_us_2.upf
N 14.0067 N.pbe-van_ak.UPF
ATOMIC_POSITIONS { crystal }
In 0.00000000000 0.00000000000 0.0000000000000
N 0.25000000000 0.25000000000 0.2500000000000
K_POINTS { automatic }
8 8 8 0 0 0
-------------------------
&inputph
tr2_ph=1.0d-14,
amass(1)=114.818,
amass(2)=14.0067,
prefix='34_vib',
fildyn='34_vib.dyn',
/
0.00 0.00 1.00
--------------------------------
&inputph
tr2_ph=1.0d-14,
amass(1)=114.818,
amass(2)=14.0067,
prefix='34_vib',
fildyn='34_vib.dyn',
/
0.00 1.00 1.00
----------------------------------
X(0,0,1)
omega( 1) = 3.163928 [THz] = 105.537987 [cm-1]
omega( 2) = 3.163928 [THz] = 105.537987 [cm-1]
omega( 3) = 6.030058 [THz] = 201.142433 [cm-1]
omega( 4) = 14.775784 [THz] = 492.870383 [cm-1]
omega( 5) = 14.775784 [THz] = 492.870383 [cm-1]
omega( 6) = 16.372030 [THz] = 546.115769 [cm-1]
X(0,1,1)
omega( 1) = 2.153190 [THz] = 71.823161 [cm-1]
omega( 2) = 2.153190 [THz] = 71.823161 [cm-1]
omega( 3) = 6.239891 [THz] = 208.141736 [cm-1]
omega( 4) = 14.879198 [THz] = 496.319913 [cm-1]
omega( 5) = 14.879198 [THz] = 496.319913 [cm-1]
omega( 6) = 16.354833 [THz] = 545.542147 [cm-1]
----------------------------------
Stefano Baroni <baroni at sissa.it> wrote:
Dear Emin, dear all: all my apologies!
Nicola was of course right, and I was WRONG! (011) IS indeed equivalent to (001), because the latter is equivalent to (-1,0,0) and the difference between (011) and (-100) is (111) which IS an FCC reciprocal-lattice vector. The coordinates of the K point are (3/4,3/4,0). With reference to the figure mentioned in the link below, K is the intersection among the planes x+y+z=3/2, z=0, and x=y, hence the above coordinates.
To come to your original question. Are the symmetries/degeneracies of the results what you expect? Can you make the input/output of your calculation accessible to us?
Stefano
On Dec 10, 2006, at 2:46 PM, e kb wrote:
Thank you for your answer Stefano,
Of course this explains the different frequencies,
and that also means that I misunderstand the kpoints given in example 5,
about band structure for an fcc,
and Dr. Marzari's explanation to another QE user,
who was confused like me.
http://www.democritos.it/pipermail/pw_forum/2006-June/004365.html
Thank you again,
Emine Kucukbenli
Stefano Baroni <baroni at sissa.it> wrote:
Emine: (001) and (011) are *NOT* two "X" points in the FCC Brillouin zone. The difference between the second and the first (010) is *NOT* a reciprocal-space vector. If it was, X would also be, which you will agree it is not. As a matter of fact, (011) has its own nickname (it is called "K"). No surprise, therefore, that frequencies @K are different from frequencies @X. Are these arguments clear and convincing enough? Stefano
On Dec 9, 2006, at 11:10 PM, e kb wrote:
Dear QE users,
I am performing phonon calculations for a zinc blende structure,
I calculated the frequencies at high symmetry points, evaluating a single point at each time.
So I followed the procedure of scf, nscf and ph.x calculation one by one for L(0.5 0.5 0.5) - Gamma - X(0,0,1) - X(0,1,1) points.
In these calculations every parameter (else than q-vector in &phonon list in nscf calculation and phonon card for ph.x input of course) is kept fixed.
Although I expect the frequencies at two X points - (0,0,1) and (0,1,1) - to be the same,
the difference in TA modes' frequencies are around 30 cm-1,
in the other ones, around 5 cm-1.
I would like to attribute this to unconverged lattice parameters, cut off energies or thresholds etc. but what I do not understand is why the program treats these two points differently, although they should be equivalent. So I expect to see the same value for frequency at these points, even if it is wrong, highly negative, or sth else that it should not be.
I will appreciate any answers.
Thank you.
Emine Kucukbenli
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Stefano Baroni - SISSA & DEMOCRITOS National Simulation Center - Trieste
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Stefano Baroni - SISSA & DEMOCRITOS National Simulation Center - Trieste
[+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)
Please, if possible, don't send me MS Word or PowerPoint attachments
Why? See: http://www.gnu.org/philosophy/no-word-attachments.html
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