[Pw_forum] Pw_forum Digest, Vol 31, Issue 2
Zhen Huang
huang87 at purdue.edu
Mon Jan 4 21:02:39 CET 2010
Dear Prof. Eyvaz Isaev and users-
This is Zhen. Thanks for you information. However, I have couple of
uncleared questions to follow up. Below is part of the results a friend of
mine provided which are the force constants of Au who has FCC structure. Two
things made me confused. First, according to your information R=(i-1)*a +
(j-1)*b + (k-1)*c, I found that 2 1 1's force constant and 4 1 1's force
constants are the same (marked by a line of @ after below). Why is this? On
the other hand, 2 2 1 should represent the force constants of x, x between
an atom and its third nearest neighbor (distance is (3/2)^0.5a where a is
the lattice constant) atom and 3 1 1 represent the force constant between an
atom and its fourth nearest neighbor (2^0.5a) (both are marked by $ below).
Why the force constant between the atoms and its third nearest neighbor is
smaller than the one between it and its fourth nearest's. Is there a
particular reason for it?
On the other hand, how do I find the R= -1*a+x*b+y*c. Seems based on
R=(i-1)*a + (j-1)*b + (k-1)*c there will never be a negative index.
*******************************
1 1 2 7.8423629 0.0000000 0.0000000 0.0000000 0.0000000
0.0000000
1 'Au ' 179527.171937097
1 1 0.0000000 0.0000000 0.0000000
F
4 4 4
1 1 1 1
1 1 1 1.26759193594E-01
2 1 1 -1.87445789062E-02 @@@@@@@@
3 1 1 1.66957109375E-03 $$$$$$$$$$$$$$
4 1 1 -1.87445789062E-02 @@@@@@@@
1 2 1 6.90391046875E-03
2 2 1 -4.25726562500E-05 $$$$$$$$$$$$$$
3 2 1 -4.96455781250E-04
4 2 1 -1.87445789063E-02
1 3 1 -2.07408906250E-04
2 3 1 -4.25726562500E-05
3 3 1 1.66957109375E-03
4 3 1 -4.25726562500E-05
1 4 1 6.90391046875E-03
2 4 1 -1.87445789063E-02
3 4 1 -4.96455781250E-04
4 4 1 -4.25726562500E-05
1 1 2 -1.87445789062E-02
******************************
Best Regards
-------
Zhen (Alex) Huang
Ph.D. Student
Nanoscale Transport Research Group
Laboratory for Computational Methods in Emerging Technologies
Cooling Technologies Research Center
School of Mechanical Engineering
Purdue University
Tel: 765 237 9733
On Sun, Jan 3, 2010 at 2:58 AM, <pw_forum-request at pwscf.org> wrote:
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> 1. Re: A question about force constants calculation output
> (Eyvaz Isaev)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sat, 2 Jan 2010 09:04:41 -0800 (PST)
> From: Eyvaz Isaev <eyvaz_isaev at yahoo.com>
> Subject: Re: [Pw_forum] A question about force constants calculation
> output
> To: PWSCF Forum <pw_forum at pwscf.org>
> Message-ID: <980073.51698.qm at web65703.mail.ac4.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
>
> Dear Zhen,
>
> In order to understand correctly the content of these files you should
> read a textbook on the lattice dynamics theory of semiconductors. Textbook
> "Fundamentals of Semiconductors" by Peter Yu and Manuel Cardona is a very
> good starting point.
>
> --- On Wed, 12/30/09, Zhen Huang <huang87 at purdue.edu> wrote:
>
> > ph.x calculation generated files alas.dynX where X goes from
> > 0 to 8. In the file alas.dyn0 it gives the k points.. Seems
> > in the other dynX files for example .dyn1 it gives force
> > constants of q=(0.0, 0.0, 0.0)? and .dyn2 gives force
> > constants of q=(-0.25?? 0.25? -0.25)
>
> This is correct. 4x4x4 set of q-points gives 8 q-points for which dynamical
> matrices have to be calculated. These q-points are written in dyn0 file.
> Files dyn1 - dyn8 are dynamical matrices.
>
> > What is the T matrix? and Matrix 1 and 2 labeled below.
>
> There is no T-matrix at all, "T" means .true., i.e. AlAs, in fact, is
> semi-conducting.
>
> Next 3x3 matrix is the macroscopic dielectric constants matrix.
>
> "Matrix 1" and "Matrix 2" contain effective Born charges for Al (atom 1)
> and As (atom 2).
>
> For metals you find "F" (.false.) and no dielectric matrix and Born
> effective charges.
>
> > Also, the questions are what is 4 4 4 representing the the force
> > constants information part labeled below,? what does the 1 1 1 1 mean >
> on the second line and also what is the meaning of the index?
> > 2?? 1?? 1? -6.26636620736E-03 (for example), I assume -6.266e-03 is
> > the force constants but what is 2 1 1.
>
> You asked this question before. Please have a look at
>
> http://www.democritos.it/pipermail/pw_forum/2008-September/010099.html
>
> The only correction is that R=(i-1)*a + (j-1)*b + (k-1)*c (thanks Stefano
> d.G).
>
> > If the forth column is the force constants why it is different from
> > Ph.x calcualtion's output.
>
> Please do not mix dynamical matrix with IFC. The first one is in q-space,
> and the second one is in R-space.
>
> > One more question, if I want to look at the force constants
> > between a unit cell and its closest nearest neibhor unit
> > cell do I look at the dynX output with k=(0, -1, 0), (-1, 0,
> > 0) and such and second nearest unit cells will be in dynX of
> > k=(0, -.5, 0), (-.5, 0, 0)?
>
> This is unclear what do you mean as IFC is for atoms, but not for unit
> cells. Just keep in mind in the Linear Response theory all calculations are
> performed inside the unit cell. To calculate the IFC range see a formula for
> R given above.
>
> 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
>
>
>
>
>
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>
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> End of Pw_forum Digest, Vol 31, Issue 2
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