You can do that using Xmgrace. In the Xmgrace GUI, go to Data > Transformations > Evaluate Expression. Then, In both the "Source" and "Destination" panes select the same set you want to convert so it is highlighted.

(As 1 ns = 1000 ps; so, 2 ps = 1/500 ns)

Finally, in the Formula box type X = X*500 then click Apply.

For installation: sudo apt install grace

User's guide:

https://plasma-gate.weizmann.ac.il/Grace/doc/UsersGuide.html

Dear Sutanu Mukhopadhyay

this is how it looks like..Is this informative??

There's something wrong in this plot. Firstly, if you've a 1 microsecond long trajectory, then in nanosecond scale, it should be 1000 ns (1 us = 1000 ns). Secondly, after changing the units, you've to change the x-axis label as well( ps to ns).

It seems that your plot is still in picosecond scale. Do the transformation and edit the x-axis label.

Dear Divya Jhinjharia

It seems that the gmx energy tool of gromacs doesn't have a flag option to choose the frequency of the output.

The best you can do in my opinion is to produce the .xvg file and then cut it down with some tool like awk, for example

$> awk 'NR%10==0' energy.xvg > new_energy.xvg

will take every 10th line of your energy file and save it in the new_energy.xvg file. If your output originally has 2ps steps and you want the values only after 10ns you have to skip 5000 points, that is

$> awk 'NR%5000==0' energy.xvg > new_energy.xvg

should produce a new_energy.xvg file with data every 10 ns. Only thing to consider should be that the first lines are comments probably starting with @ since it is an .xvg generated by gromacs, so the results will be a bit skewed, but you can modify the command to avoid the first lines.

Best

Nicola