implementing unique forces on individual atoms at each time step in a CFDEM simulation

Hi

I am trying to apply forces on atoms based on one of their coordinate positions. I have implemented this type of force successfully on a single atom using

run 50000 every 10 "fix acforce all addforce ${Force} NULL NULL region ac"

where

variable Force equal (variable function(v_xposition))

I have introduced additional atoms into the system using

read_data grann

in which I specify their positions, initial velocities, etc

To my understanding I require

variable Force atom (variable function(v_xposition)) where v_xposition is an atom type also or a vector type compute

which generates a corresponding force vector array for each atom position

I try to insert this into repeating fix

run 50000 every 10 "fix acforce all addforce Force NULL NULL region ac"

but it does not work. Can you assist me in this regard. I would like to stay away from coding at this point.

I have also investigated the possibility of doing this in a loop using equal type variables and grouping a single atom, applying the force then unfixing and ungrouping and repeating for all the atoms. I get the following output

old group != new group

Is there a way to assign new names based on the loop number or any other alternative or solution to this?

my code segment

label loop
variable i loop 7
variable xatompos equal x[$i]
variable A equal (v_function(v_xatompos[v_xatompos]))
print "Force = $A"
group atomgroup id $i
fix fixname atomgroup addforce ${A} NULL NULL region ac
unfix fixname
group atomgroup delete
next i
jump in.script loop
variable i delete

In addition when I run a coupled simulation with a single atom system the repeating fixes as previously mentioned are not accounted for. Where to account for these; In the liggghtsCommands script? And how to implement this?

Thank You