Purpose of q2r.x:

It reads force constant matrices C(q) produced by the ph.x code for a grid of q-points and calculates the corresponding set of interatomic force constants (IFC), C(R)

Input data format: [ ] = it depends

Structure of the input data: ========================================================================

&INPUT ...specs of namelist variables... /

[ nr1 nr2 nr3 nfile file(1) file(2) ... file(nfile) ]
REQUIRED
Input file name (must be specified).

"fildyn"0 contains information on the q-point grid

"fildyn"1-N contain force constants C_n = C(q_n), where n = 1,...N, where N is the number of q-points in the irreducible brillouin zone.

Normally this should be the same as specified on input to the phonon code.

In the non collinear/spin-orbit case the files produced by ph.x are in .xml format. In this case fildyn is the same as in the phonon code + the .xml extension.
REQUIRED
Output file containing the IFC in real space (must be specified)
'no'
Indicates the type of Acoustic Sum Rules used for the Born effective charges.

Allowed values:
no Acoustic Sum Rules imposed (default)
previous implementation of the asr used (3 translational asr imposed by correction of the diagonal elements of the force-constants matrix)
3 translational asr imposed by optimized correction of the IFC (projection)
3 translational asr + 1 rotational asr imposed by optimized correction of the IFC (the rotation axis is the direction of periodicity; it will work only if this axis considered is one of the cartesian axis).
3 translational asr + 3 rotational asr imposed by optimized correction of the IFC.
Note that in certain cases, not all the rotational asr can be applied (e.g. if there are only 2 atoms in a molecule or if all the atoms are aligned, etc.). In these cases the supplementary asr are cancelled during the orthonormalization procedure (see below).
set to .true. to activate two-dimensional treatment of LO-TO splitting.
.false.
set to .true. to write long-range IFC into q2r IFC file. This is required when enforcing asr='all' for infrared- active solids in matdyn. An additional column will be written for long-range part of IFC for text format, while a tag named IFC_LR will be created for xml format.
If a file "fildyn"0 is not found, the code will ignore variable fildyn and will try to read from the following cards the missing information on the q-point grid and file names:
dimensions of the FFT grid formed by the q-point grid
number of files containing C(q_n), n=1,nfile

names of the files containing C(q_n), n=1,nfile

Note that the name and order of files is not important as long as q=0 is the first.