How to switch off damping effect?

Dear community,
I used LIGGGHTS version 3.7.0 and want to run simple case (free fall by gravity of a single particle) without damping (gamma_n =0 and gamma_t = 0) , but my inputscript below doesn't work (any changes of gamma_n and gamma_t don't affect to movement) .
Can somebody help me with correct writing to change this parameters?

Best , regards Furkhat

#Contact model example

atom_style granular
atom_modify map array
boundary m m m
newton off
communicate single vel yes
units si

region reg block 0.0 0.05 0.0 0.05 0.0 0.15 units box
create_box 1 reg

neighbor 0.002 bin
neigh_modify delay 0

#Material properties required for new pair styles

fix m1 all property/global youngsModulus peratomtype 5.e6
fix m2 all property/global poissonsRatio peratomtype 0.45
fix m3 all property/global coefficientRestitution peratomtypepair 1 0.9
fix m4 all property/global coefficientFriction peratomtypepair 1 0.05
fix m5 all property/global characteristicVelocity scalar 2.
fix m6 all property/global gamman peratomtypepair 1 10.3
fix m7 all property/global gammat peratomtypepair 1 10.3

#New pair style
pair_style gran model hertz tangential history

pair_coeff * *

timestep 0.000001

fix gravi all gravity 9.81 vector 0.0 0.0 -1.0

fix xwalls1 all wall/gran model hertz tangential history primitive type 1 xplane 0.0
fix xwalls2 all wall/gran model hertz tangential history primitive type 1 xplane 0.05
fix ywalls1 all wall/gran model hertz tangential history primitive type 1 yplane 0.0
fix ywalls2 all wall/gran model hertz tangential history primitive type 1 yplane 0.05
fix zwalls1 all wall/gran model hertz tangential history primitive type 1 zplane 0.0
fix zwalls2 all wall/gran model hertz tangential history primitive type 1 zplane 0.15

create_atoms 1 single 0.025 0.025 0.1375 units box
set group all diameter 0.025 density 2500

#apply nve integration to all particles
fix integr all nve/sphere

#output settings, include total thermal energy
compute rke all erotate/sphere
thermo_style custom step atoms ke c_rke vol
thermo 100
thermo_modify lost ignore norm no
dump dmp all custom/vtk 1000 post/3_part_hertz_init_*.vtk id &
type x y z ix iy iz vx vy vz fx fy fz omegax omegay omegaz radius

run 500000 upto
unfix ins