Dear lammps users,

In my simulation I compress a nanopillar and the boundary atoms are fixed(fix 1 boundary setforce 0.0 0.0 0.0), so in order to compute the stress in the compressive direstion(say x), only mobile atoms(group mobile) need to be considered. I can use compute stress/atom command and then use compute reduce command(compute 1 mobile reduce sum c_stress[1]) to get the total x-diretion stress of the group, but how can I get the total volume of atoms in the mobile group? Since press equal stress divided by volume in lammps.

Thank you very much!

Michelle

Dear lammps users,

In my simulation I compress a nanopillar and the boundary atoms are fixed(fix

1 boundary setforce 0.0 0.0 0.0), so in order to compute the stress in

the compressive direstion(say x), only mobile atoms(group mobile) need to

be considered. I can use compute stress/atom command and then use compute

reduce command(compute 1 mobile reduce sum c_stress[1]) to get the total

x-diretion stress of the group, but how can I get the total volume of atoms

in the mobile group?

this is the million dollar question. what is the volume of an atom or a

group of atoms is not a well defined entity. if you search the mailing list

archives, you'll find numerous discussions on the subject. for confined

atoms (i.e. atoms fully surrounded by other atoms) in a regular solid or

liquid, you can use the voronoi/atom compute as an estimate, but that will

fail badly for all atoms at a surface. another option might be to look at

the USER-ATC package, which has several tools to translate atomistic

properties to a finite element grid.

axel.