[lammps-users] Different pair atom in hybrid overlay gran/hertz and colloid

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1

Dear all,

I am using hertzian spring with vdW interaction with the help of hybrid/overlay of gran/hertz/histroy and colloid.

I have two types of particles - with (1,1) - I want to use COR of 0.94 and (2,*) I want to use COR of 0.99.

I read that - gran/hertz/history is a global command and defines same coefficient for all the atoms. Do we have an option to do such that, So, I can define different gran/hertz coefficients with (2,*)

Following is my script where I am defining my potential -

pair_style hybrid/overlay gran/hertz/history 10.9 NULL 2.14 NULL 0.0 0 colloid 550.0

pair_coeff 2 2 gran/hertz/history
pair_coeff 1 2 gran/hertz/history
pair_coeff 1 1 gran/hertz/history
pair_coeff 1 1 colloid 60 1.0 49.4 49.4 550.0

Above script is working fine - Just I am not able to add different coefficients in pair_coeff 1 2 and 2 2 .

I am using the 14 May 2021 version.

Thank you in advance!.

Regards
Alok

2

Dear users,

I guess this mail is missed. If I am not clear with my query, Pls let me know.

Regards
Alok

3

since the parameters are stored with the pair style globally and not with individual pairs of atom types, you cannot, of course, change them with a pair_coeff command for different pairs of atom types. that is just logical.

thus you would have to use the sub-style multiple times in the pair_style hybrid/overlay command with different settings and then use the sub-style indexing as explained in the pair style hybrid documentation to map specific pairs of atom types to the two different sub-styles. However, I am not certain, if this can actually work for technical reasons. the gran/hertz/history pair style was most certainly not designed to be used that way.

instead, have you looked into using pair style granular instead? it is a more flexible and more recently developed DEM pair style that does allow designating different settings to pairs of atom types via pair_coeff. it is supposed to be a superset of the other granular pair styles (and then some).

axel.

4

Sorry Axel, my mistake Ill make sure to do in future.

5

I have looked into this a bit closer. The error message you report shows that your input was not correct.
If you were using the correct input you would get a different error message (about re-using a fix-ID).

With a small modification to the source code, however, this can be avoided and it looks that this will enable using the gran/hooke/history and gran/hertz/history multiple times or a combination of those in a hybrid pair style.

This modification will be made available in the next LAMMPS patch release.

axel.

6

Thanks Axel.

I also tried doing it with the new pair_style granular command.
I used granular with colloid using hybrid/overlay

I did with the following script -

7

LAMMPS is already telling you where the error is, you should not need somebody else to tell you.

The first pair_coeff command is only correct without a hybrid pair style. You must change it with. “hertz” is not a hybrid substyle. Details are in the documentation.

This is a really trivial error with an obvious fix. Please consult the manual more carefully and try more systematically to solve it yourself.
I will respond to people asking such kind of questions only a limited number of times.

8

Hi Alok,
It should be “pair_coeff * * granular hertz …”
Regards
Ting

Alok Tiwari <[email protected]>于2021年8月9日 周一下午10:33写道：

9

Thank you so much, Ting :slight_smile: You saved me!

I just realised what a stupid mistake I was doing.

Thank you Axel! You made me realise patience and a careful look at problems would have solved it.

regards
Alok