a question about compute VACF

Dear LAMMPS Users,

I have a question about the compute vacf, in this calculation is the v(0) the velocity at the beginning of the simulation or the beginning of each time step?
I mean when I use the compute from time 0 ps to 20 ps with 0.01 ps time step, is the v(0) always equals to velocity in 0 ps or it is changing each time step.
I want to calculate phonon density of states using this compute. Is this compute a good way to calculate the phonon DOS?

Thank you for your help in advance.


v(0) is the velocities at the time the compute is defined. It is mentioned right here: http://lammps.sandia.gov/doc/compute_vacf.html

You can also look at the fix phonon command.


Dear Steve,

Thank you for your response. How could I use the fix Phonon for a group of atoms? I could not find any information about creating the map file for a group of atoms.


Fix phonon takes a group as an input, as do all fixes. How it uses

the group info should be discussed on its doc page. If it’s unclear

then please send an email to the developer of the USER-PHONON

package, as listed in src/USER-PHONON/README.