Question about compute vacf

Hello LAMMPS users,

I have a question about compute vacf. In this command, we don’t specify on what timesteps the input values will be used in order to contribute to the average. In fix ave/time command, there are three parameters, i.e. Nevery, Nrepeat, and Nfreq, which controls on what time sequences the data will be used for averaging. What about compute vacf command? How can specify the mentioned parameters in this latter command?

I appreciate any help from you.

Farshad

Compute vacf merely initiates this compute and store initial
velocities, V0. Current velocities are used to calculate V*V0
whenever required by output commands. In this case, whenever Nevery,
Nrepeat and Nfreq require by fix ave/time.

Ray

Thank you Ray for your response.

OK. I think I got what you mean. First, I have to define compute vacf and then use fix ave/time to take average of vacf. Is that right?

Farshad

Compute vacf merely initiates this compute and store initial
velocities, V0. Current velocities are used to calculate V*V0
whenever required by output commands. In this case, whenever Nevery,
Nrepeat and Nfreq require by fix ave/time.

Ray

Well, you "don't have to" use fix ave/time to take average on vacf.
You can also output instantaneous values using thermo_style. The
choice of instant values or averaged values is yours.

Ray