Reconstruction of force-calculation (spring+damping)

Hello everybody,

I'm about to reconstruct the spring and damping forces in a simple 1-particle-simulation (1 particle falling on the ground) and I have a simple understanding problem:

Using the formulas from the doc pair_gran, I am not able to obtain the dumped forces by myself, which are calculated by these (basic) commands (I appended the whole input-skript in a file and in another file I appended an Excel-Calculation of the forces of that moment, when the particle touches the ground for the first time).

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atom_style granular

fix m1 all property/global youngsModulus peratomtype 5.e9
fix m2 all property/global poissonsRatio peratomtype 0.25
fix m1 all property/global coefficientRestitution peratomtypepair 1 0.05
fix m1 all property/global coefficientFriction peratomtypepair 1. 0.57

pair_style gran/hertz/history 1 0
pair_coeff * *
timestep 1e-6

fix gravi all all gravity 9.81 vector 0.0 -1.0 0.0
fix xwalls all wall/gran/hertz/history 1 0 xplane -0.1 0.1 1

fix ins nve_group pour 1 1 1 vol 0.7 1000 diam uniform 0.1 0.1 dens uniform 2500 2500 vel uniform 0. 0. -0.2 region reg

dump dmp all custom 500 ....... fy <= dumped force ------------------------------------------------------------------------------------------------------------------------------

Can anybody please help me with that problem, because I'm not sure how LIGGGHTS calculates the forces. Like I said, I used the formulas from the doc of pair_gran to calculate the normal force between wall and one particle while they are overlapping, but my results are too big.

Possible reasons:
- One reason could be some "units-conversion" I didn't notice or understand:
In the source-code of pair_gran_hertz_history.cpp I found a line (line 76) which "converts Kn and Kt from pressure units to force/distance^2" - but I don't understand the meaning of that line. Is the unit of Kn not [N/m]?
The doc of Pair_gran says: "only unit system that are self-consistent (si, cgs, lj) can be used", so I just used SI units and was expecting to get SI units in return.

- How is the Young's Modulus of the pair particle-wall calculated? In the doc there is a formula for the pair particle-particle, but not for particle-wall. I tried all possibilities, but the result didn't become more similar to the dumped forces in the dump file...

Ok, hopefully sb of you has the time to take a glance at my Excel-Calculation of the forces at timestep 148500 of the simulation. Or maybe the error is already in the input-skript?

A lot of thanks in advance,
kind regards,

Sebastian