My Community

Hi,

I am trying to get the phonon density of states (and eventually the phonon dispersion) from the new routines in vasp.6.4.1, however, when I set IBRION=5 and PHON_DOS=2, I do not see any sign of the phonons being calculated in the output.

I have attached the calculation info. What would be causing the phonons not to be calculated?

Thank you

Hi,

There are currently some limitations in the new phonon code. Notably:

• PHON_DOS requires LPHON_DISPERSION = true.
• Phonon calculations (except for zone-center phonons) require IBRION=6.

Fortunately, these limitations should be lifted in the next version of VASP. Until then, we are working on improving the documentation on the VASP wiki to reflect this.

For now, there exists a workaround if VASP is compiled with HDF5 support. See LPHON_READ_FORCE_CONSTANTS for details.

Thank you. I will attempt to summarize below and will edit if this is incorrect.

As of vasp.6.4.1, the phonon DOS can be calculated using a QPOINTS file (I got this to work initially by copying KPOINTS to QPOINTS, but that is... suboptimal), and including the following incar tags:
IBRION = 6
NFREE = 2
NSW = 1
LPHON_DISPERSION = True
PHON_DOS = 2 ! 2 is the tetrahedron method, 1 is Gaussian
PHON_NEDOS = 1000

If following the workaround from Manuel, a previous calculation can use the IBRION, NFREE, and NSW tags. Then, vaspout.h5 is copied from the precalculation to vaspin.h5 for the phonon calculation. Finally, the incar tags will be:
LPHON_DISPERSION = True
PHON_DOS = 2
PHON_NEDOS = 1000
LPHON_READ_FORCE_CONSTANTS = True

That is indeed correct. I ran a simple test with these parameters on my end and it works in both cases. Thank you for summarizing the necessary tags.