Hi,

I want to calculate the mean free path. I can calculate the electron-phonon scattering rate from the self-energies and I need the velocity matrix to calculate the mean free path as mean-free path = scattering rate*velocity. However, I cannot find the velocity matrix in the output file. Would you please let me know if I have to turn on any flag to print out the velocity matrix? Also, what will be the NAME of the output file that contains the velocity matrix as function of band index and k-points?

Thank you.

## How to print velocity Matrix

**Moderator:** hlee

### Re: How to print velocity Matrix

To clarify,

I want to calculate the electron mean free path using the EPW code. I can calculate the electron-phonon scattering rate ({tau}nk) from the self-energies and I need the electron velocity (vnk) to find the mean-free path ({tau}nk*vnk). I was searching the EPW documentation and EPW forum to find how to find the file containing the electron velocity (vnk) but did not find anything related to it. I was wondering if I need to enable any flag to print out the electron velocity (vnk)? Also, what is the name of the output file that contains the electron velocity as a function of band index and k-points?

I want to calculate the electron mean free path using the EPW code. I can calculate the electron-phonon scattering rate ({tau}nk) from the self-energies and I need the electron velocity (vnk) to find the mean-free path ({tau}nk*vnk). I was searching the EPW documentation and EPW forum to find how to find the file containing the electron velocity (vnk) but did not find anything related to it. I was wondering if I need to enable any flag to print out the electron velocity (vnk)? Also, what is the name of the output file that contains the electron velocity as a function of band index and k-points?