any specific command for different size particle???

use fix particletemplate/sphere (https://www.cfdem.com/media/DEM/docu/fix_particletemplate_sphere.html)
to define different particles with different radii and densities like

fix pts1 all particletemplate/sphere 15485863 atom_type 1 density constant 2500 radius constant 0.0015
fix pts2 all particletemplate/sphere 15485867 atom_type 1 density constant 2500 radius constant 0.0025
fix pts3 all particletemplate/sphere rand_num3 atom_type 1 density constant 2500 radius constant 0.0035
fix pts4 all particletemplate/sphere rand_num4 atom_type 1 density constant 2500 radius constant 0.0045
fix pts5 all particletemplate/sphere rand_num5 atom_type 1 density constant 2500 radius constant 0.0055

then create the distribution using fix particledistribution/discrete
fix pdd1 all particledistribution/discrete 32452843 5 pts1 0.2 pts2 0.2 pts3 0.2 pts4 0.2 pts5 0.2
here, all five sizes have the same probability (0.2) of being inserted

Hello,

Like yourself, I would also like some clarity on how to introduce different properties between particles-particle and particle wall.
I haven't came across any examples that specify this.

Thanks,

Using
fix m1 all property/global youngsModulus peratomtype 5.e6 5.e6
is saying that you have 2 different materials. One with a youngs modulus of 5e6 and another with 5e6
this is repeated for m2.

Using
fix m3 all property/global coefficientRestitution peratomtypepair 2 0.5 0.3 0.3 0.08
says that I would like the coefficient of restitution to be 0.5 when material 1 hits material 1
says that I would like the coefficient of restitution to be 0.3 when material 1 hits material 2
says that I would like the coefficient of restitution to be 0.3 when material 2 hits material 1
says that I would like the coefficient of restitution to be 0.08 when material 2 hits material 2
similarly with m4 and m5
Notice that material 1 can be used for either an atom or for geometry.

As an example, one material could be granite and the other could be coal. Now during your simulation, you may want to use atoms of different sizes for both coal and granite.
This DOES NOT change their material properties. So if I wanted 3 different sizes of coal and 4 different sizes of granite, I would use the commands

fix pts1 all particletemplate/sphere 15485863 atom_type 1 density constant ${coal_density} radius constant 0.0015
fix pts2 all particletemplate/sphere 15485867 atom_type 1 density constant ${coal_density} radius constant 0.0025
fix pts3 all particletemplate/sphere ${rand_num3} atom_type 1 density constant ${coal_density} radius constant 0.0035
fix pts4 all particletemplate/sphere ${rand_num4} atom_type 2 density constant ${granite_density} radius constant 0.0025
fix pts5 all particletemplate/sphere ${rand_num5} atom_type 2 density constant ${granite_density} radius constant 0.0035
fix pts6 all particletemplate/sphere ${rand_num6} atom_type 2 density constant ${granite_density} radius constant 0.0045
fix pts7 all particletemplate/sphere ${rand_num7} atom_type 2 density constant ${granite_density} radius constant 0.0055

Now we need to tell the program how to insert these atoms randomly into our system
say I want
pts1 to be used 2% of the time
pts2 to be used 4% of the time
pts3 to be used 6% of the time
pts4 to be used 10% of the time
pts5 to be used 30% of the time
pts6 to be used 35% of the time and
pts7 to be used 13% of the time
I would use the command
fix pdd1 all particledistribution/discrete 32452843 7 pts1 0.02 pts2 0.04 pts3 0.06 pts4 0.10 pts5 0.30 pts6 0.35 pts7 0.13