Dear all

hope you are all well recently, I hope to obtain some help for the mixing of coefficients of pair_style granular. I hope to have two different materials, but both the “hertz/material” model.

for material 2, i hope to have “rolling” part, while material 1 dose not have “rolling” part.

but this cannot really work in the lastest lammps by default mixing by lammps, therefore, i wish to give the “pair_coeff 1 2” by myself and want to give pair_coeff 1 2 without “rolling” part, but the remaining parameters just follow the equation for lammps documentations:

https://docs.lammps.org/pair_granular.html

however, i do meet a problem for Young’s modulus of pair_coeff 1 2. Firstly, for the equations of effective young’s modulus, there are two different equations for E_eff,ij; see equation 2 and 3 in the image.

i attached the image (from lammps documentations) for these two equations. I am not pretty sure whether this is a typo for the equation 3, whether the square is missing in the equation 3.

So I assume that the equation 2 is right. So in my case, i tried to check this without “rolling” part;

so input script 1, the mixing coefficients are automatically obtained by LAMMPS; input script 2, i give

the mixing coefficients based on the equations from LAMMPS documentations. I think i should get the 100% same results.

for my material 1, E1 = 7e6, v1 = 0.5; material 2, E2 = 7e10, v2 = 0.2, so based on equation 1, the Eeff,ij = 9.33e6; then i should give the suitable Eij so that i obtain the same Eeff,ij (9.33e6), based on my calculation from equation 2, when Eij is 1.68e7, the Eeff,ij is 9.33e6, which should be ok, but it seems that i got totally different simulations results for these input script 1 and input script 2:

see input 1, the key sentences are:

```
pair_coeff 2 2 hertz/material 7.0e10 0.1 0.2 tangential mindlin_rescale/force NULL 1.0 1.0
pair_coeff 1 1 hertz/material 7e6 0.5 0.5 tangential mindlin_rescale/force NULL 1.0 0.001
```

see input 2, the key sentences are :

```
pair_coeff 2 2 hertz/material 7.0e10 0.1 0.2 tangential mindlin_rescale/force NULL 1.0 1.0
pair_coeff 1 1 hertz/material 7e6 0.5 0.5 tangential mindlin_rescale/force NULL 1.0 0.001
pair_coeff 1 2 hertz/material 1.68e7 0.316228 0.316228 tangential mindlin_rescale/force NULL 1.0 0.031623
```

all parameters are geometric averaging, and Eij is calculated based on equation 1,2 and 3.

so does anyone has the idea that how should i correctly give the values for mixing of coefficients, i just want to obtain the same results compared to the default results obtained from lammps

thanks for your time,

hope you all have a nice day