hooke/stiffness model

1. Whenever am I trying to run simulation using the hooke/stiffness model with the code give below the particles are passing through the zwall which they shouldn't. Can anyone please clarify that what is wrong with this code?

2. Can I define new model instead of using the predefined model for granular contact ?

3. While using the absolute_damping off in hooke/stiffness model, Is it possible to change the given formula for gamma_n i.e. from given formula (gamma_n-specified)*(m_effective) to (gamma_n_specified)* (m_effective)^(0.5).

4. If I have normal distribution or some other distribution (number of particles vs radius of particle) for particle size distribution. Can I use that distribution while giving the particle distribution in LIGGGHTS?

#Simple chute wear test

atom_style granular
atom_modify map array
boundary p p f
newton off

communicate single vel yes

units si

region reg block 0.0 0.08 0.0 0.08 0.0 0.15 units box

create_box 1 reg

neighbor 0.001 bin
neigh_modify delay 0

#Material properties required for new pair styles

fix a1 all property/global kn peratomtypepair 1 2e5
fix a2 all property/global kt peratomtypepair 1 6e4
fix a3 all property/global gamman peratomtypepair 1 3e7
fix a4 all property/global gammat peratomtypepair 1 3e7
fix a5 all property/global gamman_abs peratomtypepair 1 3e7
fix a6 all property/global gammat_abs peratomtypepair 1 3e7

#New pair style
pair_style gran model hooke/stiffness absolute_damping on #Hooke without cohesion
pair_coeff * *

timestep 0.00001

fix gravi all gravity 10 chute 20

#the plane
fix zwall all wall/gran model hooke/stiffness primitive type 1 zplane 0.0

#distributions for insertion
fix pts1 all particletemplate/sphere 1 atom_type 1 density constant 8000 radius constant 0.002
fix pdd1 all particledistribution/discrete 1 1 pts1 1.0

#region and insertion
group nve_group region reg
region insert block 0.035 0.055 0.035 0.055 0.1 0.12 units box

#particle insertion
fix ins nve_group insert/rate/region seed 5101 distributiontemplate pdd1 &
nparticles 500 massrate 70 insert_every 10 overlapcheck yes all_in no vel constant 0.0 0.0 -0.005 &
region insert

#apply nve integration to all particles that are inserted as single particles
fix integr nve_group nve/sphere

#output settings, include total thermal energy
compute 1 all ke
thermo_style custom step atoms cpu ke
thermo 1000
thermo_modify lost ignore norm no
compute_modify thermo_temp dynamic yes

#insert the first particles so that dump is not empty
run 1
dump dmp1 all custom 100 post/dump*.xyz id type x y z vx vy vz
dump_modify dmp1 sort 1
dump pic all image 500 images/img*.ppm type type size 512 512 adiam 0.004
#insert particles
run 200000 upto
unfix ins