How to define force property on a atom in a trajectory file?

Hi everyone,
I am using gulp to conduct dynamics simulation, there is a generated trajectory file (.trj)after the job is finished, i want to know the forces on atoms in the X,Y,Z directions, but when i clicked on one atom and looked at the Proprtties explorer (filter by atom), found that there was no force property. How come?
Or what should i type in the input file before the job gets started?
Is there anyone who can provide some advice regarding this?

Thanks a lot in advance!

Best regards,
Weifu