Guide about the Phonon calculations (using PHONON software)

To calculate the phonon properties, there are 3 main softwares interfaced to wien2k code: PHONON by K.Parlinski, PHONOPY by A.togo and  PHON by D.Alfè .


The softawre PHONON is not a free but there is a demo version that can do calculation for Fm-3m space group ( wien list mailing ).

There are version for MS.Windows and for Linux ( site ) but the most used is the version of the Windows.

 NB: What's exists in the wien2k package is the PHONON interface for the wien2k code and it's not the software itself.

Procedure using PHONON code:

You would define the structure of your compound in PHONON together with a supercell of suf- ficient size (e.g. 64 atoms). PHONON will then generate a list of necessary displacements of the individual atoms. 

To use the PHONON software follow the steps in the following link:

http://wolf.ifj.edu.pl/workshop/work2004/files/talks/Parlinski_krakow_2004.pdf 

The resulting file case.d45 must be transfered to UNIX. Here you would run WIEN2k-scf calculations for all displacements and collect the resulting forces, which will be transfered back to PHONON (case.dat and/or case.dsy). With these force information PHONON calculates phonon at arbitrary q-vectors together with several thermodynamic properties.

  init_phonon_lapw

 init_phonon_lapw uses case.d45 from PHONON and creates subdirectories case_XX and case_XX.struct files for all required displacements. It allows you to define globally RMT values for the different atoms and

- initializes every case individually (batch option of init lapw is now supported) 

or 

- initializes every second case (useful for pos. and neg. displacements, which have the same symmetry and thus only one initialization is necessary), or 

- initializes only the first case and copies the files from the first case to all others. This is most convenient in low symmetry cases with P1 symmetry for all cases and thus just one init lapw needs to be executed (while for higher symmetry a separate initialization is required (but computational effort is reduced). 

Please use mainly nn to reduce equivalent atoms. sgroup might change the unitcell and than the collection of forces into the original supercell is not possible (or quite difficult). 

A script run phonon has been created. Modify it according to your needs (parallelization,....) and run all cases to selfconsistency. 

Note that good force convergence is essential (at least 0.1 mRy/bohr) and if your structure has free parameters, either very good equillibrium positions must have been found before, or even better, use both, positive and negative displacements to average out any resulting error from nonequillibrium positions. 

analyse_phonon_lapw 

analyse phonon lapw uses the resulting scf files and generates the “Hellmann-Feynman”-file required by PHONON. When you have positive and negative displacements an automatic averaging will be performed. The resulting case.dat and case.dsy filse should be transfered back to MS-Windows and imported into PHONON. 

Summary:

- Defining the structure of the compound with PHONON ----> case.d45
- Transferring the case.d45 file to Unix in new directory
- In terminal run:
                         * init_phonon_lapw ---> case_xx and case_xx.struct files
                         * run_phonon to be modified and executed
                         * analyse_phono_lapw  ---> case.dat and case.dsy

- Transferring back the new files case.dat and case.dsy to the PHONON software.