# [Pw_forum] IFC's

Katalin Gaal-Nagy katalin.gaal-nagy at physik.uni-regensburg.de
Mon Sep 3 10:43:43 CEST 2007

```Dear all,

the message I send just half an hour ago is held because of the size ...
However, I resend it without the attachments. If anyone is interested in
the files with the routines, please tell me!

Best wishes,
Katalin

---------- Forwarded message ----------
Date: Mon, 3 Sep 2007 10:01:59 +0200 (CEST)
From: Katalin Gaal-Nagy <katalin.gaal-nagy at physik.uni-regensburg.de>
To: PWSCF Forum <pw_forum at pwscf.org>
Subject: Re: [Pw_forum] IFC's

well ... you can do it, with a trick.
If I understood correctly, you have the q points on a 3x3x3 grid and the q
points on a 4x4x4 grid. A grid containing both sets of q points is the 12x12x12
grid.
You can do the following: You calculate the force constants of the 4x4x4 grid
and do a back Fourier transform and calculate the dynamical matrices on a
12x12x12 grid. In this set of dynamical matrices, the ones corresponding to the
4x4x4 grid are identical (up to numerical noise, which is little). Then you
take these  12x12x12 interpolated dynamical matrices, throw away the
interpolated ones corresponding to the 3x3x3 mesh and put instead the 3x3x3
ones you have calculated with ph.x. You again have a full set of dynamical
matrices and you can calculate from these the force constants, which correspond
to a mixing of a 4x4x4 grid and a 3x3x3 grid. Note, they DON'T correspond to a
12x12x12 grid, since there are still interpolated dynamical matrices left. With
the resulting dynamical matrices also no physical meaning like range of
corresponding forces can be connected any more.

The idea of this scheme can be found under condmat arXiv:0707.0384.

For the use of this scheme I modified the postprocessing routines matdyn.f90 of
ESPRESSO (I am not sure about the version, if should have been espresso-3.1). I
don't remember, if I was putting it in a nice, commented shape (for sure tha
Makefile not ... ). The main modification was to tell the code to write out the
dynamical matrices for all q in star(q) in a way, that q2r.x can read it again.
The modified routines and a makefile are attached. I would apprechiate if you
could test, if the compilation is working.

However, you have to use the routines q2r.x and matdyn.x ...
The matdyn.x has now an additional flag and the input reads as

&input
asr='simple',  amass(1)=28.086,
flfrc='si.q888.force',
flfrq='si.q16.16.16.freq.interpol',
dynmatout=.true.
/
349

.... list of k points created with kpoints.x ...

It creates (in this case) 349 files containing the interpolated dynamical
matrices dynint.\$number where \$number is the number of the q point given in the
list ...

Paolo, in case you want to include it to the ESPRESSO paackage and there are

Good luck,
Katalin

On Sun, 2 Sep 2007, Paolo Giannozzi wrote:

>
> On Sep 2, 2007, at 10:25 , Ezad Shojaee wrote:
>
>> i want to know that are we able to use the 'IFC's calculated with
>> two grids' together? for example we calculate them by a 3*3*3 grid,
>> and then 4*4*4 , then use all of them in calculating C(q) for an
>> arbitrary point in the Brillouin zone?
>
> no, it is not: you can use only one specific grid. In principle one
> could
> a denser grid, I think, but it would be a mess
>
> Paolo
> ---
> Paolo Giannozzi, Democritos and University of Udine, Italy
>
>
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