forked from lijiext/lammps
76 lines
1.9 KiB
Plaintext
76 lines
1.9 KiB
Plaintext
.. index:: newton
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newton command
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==============
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Syntax
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""""""
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.. parsed-literal::
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newton flag
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newton flag1 flag2
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* flag = *on* or *off* for both pairwise and bonded interactions
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* flag1 = *on* or *off* for pairwise interactions
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* flag2 = *on* or *off* for bonded interactions
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Examples
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""""""""
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.. parsed-literal::
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newton off
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newton on off
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Description
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"""""""""""
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This command turns Newton's 3rd law *on* or *off* for pairwise and
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bonded interactions. For most problems, setting Newton's 3rd law to
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*on* means a modest savings in computation at the cost of two times
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more communication. Whether this is faster depends on problem size,
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force cutoff lengths, a machine's compute/communication ratio, and how
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many processors are being used.
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Setting the pairwise newton flag to *off* means that if two
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interacting atoms are on different processors, both processors compute
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their interaction and the resulting force information is not
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communicated. Similarly, for bonded interactions, newton *off* means
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that if a bond, angle, dihedral, or improper interaction contains
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atoms on 2 or more processors, the interaction is computed by each
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processor.
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LAMMPS should produce the same answers for any newton flag settings,
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except for round-off issues.
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With :doc:`run_style <run_style>` *respa* and only bonded interactions
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(bond, angle, etc) computed in the innermost timestep, it may be
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faster to turn newton *off* for bonded interactions, to avoid extra
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communication in the innermost loop.
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Restrictions
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""""""""""""
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The newton bond setting cannot be changed after the simulation box is
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defined by a :doc:`read_data <read_data>` or
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:doc:`create_box <create_box>` command.
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Related commands
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""""""""""""""""
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:doc:`run_style <run_style>` respa
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Default
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"""""""
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.. parsed-literal::
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newton on
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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Section_commands.html#comm
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