To calculate the Phonon Properties there are 2 methods:

1. The DFPT method

2. The supercell method: It's time consuming and needs sufficient memory

 

In this tutorial, we will use the DFPT method which is the default choice of the Phonon task to calculate the Phonon band structure and the phonon DOS of Silicon.

 Input files

 Si_DFPT.cell 

%block lattice_cart
2.7 2.7 0.0
2.7 0.0 2.7
0.0 2.7 2.7
%endblock lattice_cart

%block positions_frac
Si 0.00 0.00 0.00
Si 0.25 0.25 0.25
%endblock positions_frac

kpoints_mp_grid 5 5 5
phonon_kpoint_mp_grid 5 5 5   ! Generate MP grid of phonon q-points

symmetry_generate            ! Find symmetry operations of crystal structure

%block species_pot
NCP
%endblock species_pot

 

Si_DFPT.param 

task             : PHONON    ! Choose a phonon calculation
phonon_method    : DFPT      ! It's the default method
xc_functional    : LDA
opt_strategy     : SPEED     ! Optimise for speed over memory saving
cut_off_energy   : 700.0 eV  ! Plane-wave cutoff for this system
elec_method      : DM        ! Use fast DM solver even for insulating system
calculate_born_charges : false
phonon_calc_lo_to_splitting : false
efield_calc_ion_permittivity : false

 

Si_Dispersion.cell

%block lattice_cart
2.7 2.7 0.0
2.7 0.0 2.7
0.0 2.7 2.7
%endblock lattice_cart

%block positions_frac
Si 0.00 0.00 0.00
Si 0.25 0.25 0.25
%endblock positions_frac

kpoints_mp_grid 5 5 5
phonon_kpoint_mp_grid 5 5 5     ̣
phonon_kpoint_mp_offset : INCLUDE_GAMMA

%block phonon_fine_kpoint_path
0.500000 0.500000 0.500000
0.000000 0.000000 0.000000
0.500000 0.000000 0.500000
0.500000 0.250000 0.750000
0.375000 0.375000 0.750000
%endblock phonon_fine_kpoint_path

symmetry_generate

%block species_pot
NCP
%endblock species_pot

 

 Si_Dispersion.param

task : Phonon
phonon_method : DFPT      ! It's the default method
fix_occupancy : true
continuation  : Si_DFPT.check
phonon_fine_method : interpolate

 

Si_DoS.cell 

%block lattice_cart
2.7 2.7 0.0
2.7 0.0 2.7
0.0 2.7 2.7
%endblock lattice_cart

%block positions_frac
Si 0.00 0.00 0.00
Si 0.25 0.25 0.25
%endblock positions_frac

kpoints_mp_grid 5 5 5
phonon_kpoint_mp_grid 5 5 5     ̣
phonon_kpoint_mp_offset : INCLUDE_GAMMA

phonon_fine_kpoint_mp_grid 25 25 25

symmetry_generate

%block species_pot
NCP
%endblock species_pot

 

Si_DoS.param

task : Phonon
phonon_method : DFPT      ! It's the default method
fix_occupancy : true
continuation  : Si_DFPT.check
phonon_fine_method : interpolate

 Execution 

$ mpirun -np 4 castep.mpi Si_DFPT
$ mpirun -np 4 castep.mpi Si_Dispersion

$ mpirun -np 4 castep.mpi Si_DoS

 

 Plotting  

$ dispersion.pl -sym fcc -xg Si_Dispersion.phonon

$ dos.pl -xg Si_DoS.phonon -w 0.3

 

We get the following plots

 

References:

 https://www-users.york.ac.uk/~mijp1/teaching/grad_FPMM/practical_classes/Practical_6.pdf

https://www-users.york.ac.uk/~mijp1/teaching/grad_FPMM/lecture_notes/lec13_14_phonons.pdf 

https://www.isis.stfc.ac.uk/Pages/lattice-dynamics-and-spectroscopy-from-dft13038.pdf 

https://castep-docs.github.io/castep-docs/documentation/Phonons/Castep_Phonons/Running-phonon-calculations/ 

https://www.tcm.phy.cam.ac.uk/castep/Phonons_Guide/2-sec:examples.html?fbclid=IwY2xjawJPsZFleHRuA2FlbQIxMAABHZfv_bLAsZZ_7itZIfBI18iz3iYXru04HO64BGLm17H9ndDgPubGDKqZAw_aem_tZpXehm7yytusOU0QDKi8w