I have a simple question about calculation of phonon band structure. Suppose we have a super huge model. Can we compute only first few dispersion curves? I only need the phonon bands at low frequency. So, I am looking for any keyword that can be used to speed up the calculation. Any comment will be greatly appreciated!
If your system is very large then the dispersion will be pretty flat and so you might be able to get away with a gamma point calculation which will be cheaper. The acoustic modes (which will show the most dispersion) can characterised via a property calculation which gives the wave velocities in this limit without the need for phonons. Unfortunately at the moment there is no option in GULP to only calculate selected eigenvalues from the phonon spectrum at present. However you can modify the calls to Lapack to invoke variants that give selected eigenvalues with a small modification of the code. You can also speed up the execution by using more cores in parallel. You may want to look at the recent thread on memory allocation errors which also relates to run massive systems in a phonon calculation.
Thank you for the information. I just followed manual and reinstalled GULP for parallel computation. Only need to edit mkgulp file. It works fine now! Thank you again for your help!