forked from lijiext/lammps
60 lines
2.0 KiB
Plaintext
60 lines
2.0 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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compute stress/atom command :h3
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[Syntax:]
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compute ID group-ID stress/atom :pre
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ID, group-ID are documented in "compute"_compute.html command
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stress/atom = style name of this compute command :ul
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[Examples:]
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compute 1 mobile stress/atom :pre
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[Description:]
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Define a computation that computes the per-atom stress tensor for each
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atom in a group. The 6 components can be output via the "dump
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custom"_dump.html command.
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The stress tensor is computed for only pairwise forces where the {ab}
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component of stress on atom {i} is given by
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:c,image(Eqs/stress_tensor.jpg)
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where the first term is a kinetic energy component for atom {i}, {j}
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loops over the {N} neighbors of atom {i}, and {Fb} is one of 3
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components of force on atom {i} due to atom {j}. Both {a} and {b}
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take on values x,y,z to generate the 6 components of the symmetric
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tensor.
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Note that this formula for stress does not include virial
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contributions from intra-molecular interactions (e.g. bonds, angles,
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torsions, etc). Also note that this quantity is the negative of the
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per-atom pressure tensor. It is also really a stress-volume
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formulation. It would need to be divided by a per-atom volume to have
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units of stress, but an individual atom's volume is not easy to
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compute in a deformed solid. Thus, if you sum the diagonal components
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of the per-atom stress tensor for all atoms in the system and divide
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the sum by 3V, where V is the volume of the system, you should get -P,
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where P is the total pressure of the system.
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Computation of per-atom stress tensor components requires a loop thru
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the neighbor list and inter-processor communication, so it can be
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inefficient to compute/dump this quantity too frequently or to have
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multiple compute/dump commands, each of a {stress/atom} style.
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[Restrictions:] none
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[Related commands:] none
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[Default:] none
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