Construction of an amorphous cell for DPD study

Hello everyone,
I am performing a DPD simulation of a polyethylene chain with 40 monomer units.I perform the following steps:
1.Amorphous cell construction
2.Equilibration in forcite
3.DPD run
In order to ensure that the  number density of DPD particles is 3,
Is it required to construct an amorphous cell  with dimensions which is equal to the DPD length unit?

Thanks,
Deepa