Band unfolding for phonons <http://yuzie007.github.io/upho/>

• numpy
• h5py
• phonopy>=2.3.2

pip install git+https://github.com/yuzie007/upho.git@v0.6.1

Here we consider the hypothetical case when Cu_3Au with the L2_1 structure is regarded as a random configuration of the A1 (fcc) structure.

1. Create FORCE_SETS file for the structure (maybe including disordered chemical configuration) you want to investigate using phonopy in an usual way. Be careful that the number of the structures with atomic displacements to get FORCE_SETS can be huge (~100) for a disordered configuration.

2. Create FORCE_CONSTANTS file from FORCE_SETS file using phonopy as:

   phonopy writefc.conf
   

   where writefc.conf is a text file like:

   FORCE_CONSTANTS = WRITE
   DIM = 2 2 2
   

   DIM must be the same as that what you used to get FORCE_SETS.

3. Prepare two VASP-POSCAR-type files, "POSCAR" and "POSCAR_ideal". POSCAR includes the original chemical configuration, which may be disordered.:

   Cu Au
      1.00000000000000
        3.7530000000000001    0.0000000000000000    0.0000000000000000
        0.0000000000000000    3.7530000000000001    0.0000000000000000
        0.0000000000000000    0.0000000000000000    3.7530000000000001
      Cu   Au
        3     1
   Direct
     0.0000000000000000  0.5000000000000000  0.5000000000000000
     0.5000000000000000  0.0000000000000000  0.5000000000000000
     0.5000000000000000  0.5000000000000000  0.0000000000000000
     0.0000000000000000  0.0000000000000000  0.0000000000000000
   

   Note that although FORCE_CONSTANTS may be obtained using relaxed atomic positions, here the positions must be the ideal ones.

   POSCAR_ideal is the ideal configuration, from which the crystallographic symmetry is extracted.:

   X
      1.00000000000000
        3.7530000000000001    0.0000000000000000    0.0000000000000000
        0.0000000000000000    3.7530000000000001    0.0000000000000000
        0.0000000000000000    0.0000000000000000    3.7530000000000001
       X
        4
   Direct
     0.0000000000000000  0.5000000000000000  0.5000000000000000
     0.5000000000000000  0.0000000000000000  0.5000000000000000
     0.5000000000000000  0.5000000000000000  0.0000000000000000
     0.0000000000000000  0.0000000000000000  0.0000000000000000
   

   In this file I recommend to use dummy symbols like 'X' to avoid confusion.

4. Prepare band.conf file including something like:

   DIM =  2 2 2
   PRIMITIVE_AXIS =  0 1/2 1/2  1/2 0 1/2  1/2 1/2 0
   BAND =   0 0 0  0 1/2 1/2, 1 1/2 1/2  0 0 0  1/2 1/2 1/2
   BAND_POINTS = 101
   BAND_LABELS =  \Gamma X \Gamma L
   FORCE_CONSTANTS = READ
   

   The style is very similar to that of phonopy conf files, but be careful about the following tags.

   DIM describes the expansion from the original POSCAR to the POSCARs with atomic displacements used to get FORCE_SETS. Therefore, this should be the same as the phonopy option when creating the structures with atomic displacements (1).

   PRIMITIVE_AXIS is the conversion matrix from POSCAR_ideal to the the primitive cell you expect.

4. Run:

   upho_weights band.conf
   

   then you hopefully get band.hdf5 file.

5. Run:

   upho_sf --fpitch 0.01 -s 0.05 --function lorentzian --format text
   

   then you hopefully get sf_E1.dat, sf_E2.dat, and sf_SR.dat files. In these files, the first, second, and third columns are for distances in reciprocal space, frequencies, and the values of spectral functions, respectively.

Atomic masses whose sites are equivalent in the underlying structure are averaged.

FC elements which are equivalent under the symmetry operations for the underlying structure are averaged.

Filename for the weights data.

Output file format.

Function used for the smearing.

Paramter for the smearing function (THz). For Gaussian, this is the standard deviation. For Lorentzian, this is the HWHM (gamma).

Maximum frequency (THz).

Minimum frequency (THz).

Frequency pitch (THz).

Use squared frequencies instead of raw frequencies.

(Projective) representations of little cogroup may be treated in a wrong way when we consider wave vectors on the BZ boundary and translational parts of symmetry operations are not equal to zero.

Yuji Ikeda (y.ikeda@mpie.de, Max-Planck-Institut für Eisenforschung GmbH, Germary)

When using this code, please cite the following article.

Mode decomposition based on crystallographic symmetry in the band-unfolding method, Yuji Ikeda, Abel Carreras, Atsuto Seko, Atsushi Togo, and Isao Tanaka, Phys. Rev. B 95, 024305 (2017). http://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.024305