Dear Prof. Eyvaz Isaev,
Thanks for your answering and instruction.
I haved downloaded examples_disp.tgz through the site
www.quantum-espresso.org and learn how to calculate phonon dispersion curves
with that routine. But since I cann't run the programs in a parallel style,it
will be time-consuming calculating with that way.(But I can submit many jobs. I
cann't compile the source in a parallel style.)
So I wonder if I can calculate the F(q) for each required q-points then get
the files dyn1:10 together, and run q2r.x, matdyn.x to get the phonon
dispersions.
Actually I have runned in this way with the ph.in files setted such as
ldisp=.false.
/
0.0 0.0 0.0 (other points)
and I got the dyn files, the CdCNi3-444.fc file and the CdCNi3-444.freq file in
the right format. But there are negative frequencies in them.
So I wonder if there are some underlying settings different between
ldisp=.true. and ldisp=.false. , so I tried ph.in files in the former one. And
I get the reported problem.
Right yesterday I learned from the site www.quantum-espresso.org(F.A.Q.) that
negative frequencies may be resulted from a non-converged groundstate (Ecut,
#k, ...). Maybe I set the ecut and k-grid too small. But the reported problem
still be. So is my settings wrong or there is a flaw in the ph.x ?
Best regards,
li-ming-fan
?2008-12-29?"Eyvaz Isaev" ???
>Dear li-ming-fan,
>
>In order to calculate phonon dispersion curves you need to calculate real
>space Interatomic Force Constants matrix F(R). This can be obtained via the
>FFT using the dynamical matricies F(q).
>
>In order to get F(q) set, you should use only nq1,nq2,nq3, but not iq1,iq2,iq3
>which are used to calculate F(q) for a given q-point(s).
>
>After F(q)=> F(R) transformation you have to supply a list of q-points along
>high symmetry directions and calculate phonon modes for these points.
>
>Bests,
>Eyvaz.
>
>
>---
>Prof. Eyvaz Isaev,
>Theoretical Physics Department, Moscow State Institute of Steel & Alloys,
>Russia,
>Department of Physics, Chemistry, and Biology (IFM), Linkoping University,
>Sweden
>Condensed Matter Theory Group, Uppsala University, Sweden
>Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com
>
>
>--- On Mon, 12/29/08, lzh-ming wrote:
>
>> From: lzh-ming
>> Subject: [Pw_forum] problem about calculation with ph.x
>> To: "Pw_forum"
>> Date: Monday, December 29, 2008, 2:46 PM
>> Hello everyone,
>> I have tried to calculate the phonon disperation of
>> CdCNi3.
>> I wrote in the file CdCNi3.ph.in as follow:
>>
>> ldisp=.true.,
>> nq1=4, nq2=4, nq3=4,
>> iq1=2, iq2=1, iq3=1,
>>
>> but in the file CdCNi3.dyn0 , I got
>> 4 4 4
>> 1
>> 0.0 0.0 0.0
>>
>> I changed the value of iq1,iq2,iq3 to 2,2,1, I still got
>> 0.0 0.0 0.0.
>> I set the value as 3 3 2, I got 0.25 0.25 0.25.
>> When the value is 3 3 3, I got -0.5 -0.5 -0.5.(This is
>> right.)
>>
>> I tried all the 10 unequivalent points of 4*4*4 grid(simple
>> cube),
>> I only got 3 different outputs.
>>
>> What's the problem? Can you help me?
>>
>> Thanks a lot!
>>
>> li-ming-fan
>>
>>
>>
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>
>
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