136 lines
4.9 KiB
ReStructuredText
136 lines
4.9 KiB
ReStructuredText
.. index:: compute stress/cylinder
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.. index:: compute stress/spherical
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compute stress/cylinder command
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=================================
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compute stress/spherical command
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==================================
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Syntax
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""""""
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.. code-block:: LAMMPS
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compute ID group-ID style args
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* ID, group-ID are documented in :doc:`compute <compute>` command
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* style = stress/spherical or stress/cylinder
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* args = argument specific to the compute style
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.. parsed-literal::
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*stress/cylinder* args = zlo zh Rmax bin_width keyword
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zlo = minimum z-boundary for cylinder
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zhi = maximum z-boundary for cylinder
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Rmax = maximum radius to perform calculation to
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bin_width = width of radial bins to use for calculation
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keyword = ke (zero or one can be specified)
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ke = yes or no
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*stress/spherical*
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x0, y0, z0 = origin of the spherical coordinate system
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bin_width = width of spherical shells
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Rmax = maximum radius of spherical shells
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Examples
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""""""""
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.. code-block:: LAMMPS
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compute 1 all stress/cylinder -10.0 10.0 15.0 0.25
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compute 1 all stress/cylinder -10.0 10.0 15.0 0.25 ke no
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compute 1 all stress/spherical 0 0 0 0.1 10
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Description
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"""""""""""
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Compute *stress/cylinder*, and compute
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*stress/spherical* define computations that calculate profiles of the
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diagonal components of the local stress tensor in the specified
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coordinate system. The stress tensor is split into a kinetic
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contribution :math:`P^k` and a virial contribution :math:`P^v`. The sum
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gives the total stress tensor :math:`P = P^k+P^v`. These computes can
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for example be used to calculate the diagonal components of the local
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stress tensor of surfaces with cylindrical or spherical
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symmetry. These computes obeys momentum balance through fluid
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interfaces. They use the Irving--Kirkwood contour, which is the straight
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line between particle pairs.
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The compute *stress/cylinder* computes the stress profile along the
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radial direction in cylindrical coordinates, as described in
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:ref:`(Addington)<Addington1>`. The compute *stress/spherical*
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computes the stress profile along the radial direction in spherical
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coordinates, as described in :ref:`(Ikeshoji)<Ikeshoji4>`.
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Output info
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"""""""""""
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The default output columns for *stress/cylinder* are the radius to the
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center of the cylindrical shell, number density, :math:`P^k_{rr}`,
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:math:`P^k_{\phi\phi}`, :math:`P^k_{zz}`, :math:`P^v_{rr}`,
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:math:`P^v_{\phi\phi}`, and :math:`P^v_{zz}`. When the keyword *ke* is
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set to *no*, the kinetic contributions are not calculated, and
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consequently there are only 5 columns: the position of the center of the
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cylindrical shell, the number density, :math:`P^v_{rr}`,
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:math:`P^v_{\phi\phi}`, and :math:`P^v_{zz}`. The number of bins (rows) is
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:math:`R_\text{max}/b`, where :math:`b` is the specified bin width.
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The output columns for *stress/spherical* are the position of the center
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of the spherical shell, the number density, :math:`P^k_{rr}`,
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:math:`P^k_{\theta\theta}`, :math:`P^k_{\phi\phi}`, :math:`P^v_{rr}`,
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:math:`P^v_{\theta\theta}`, and :math:`P^v_{\phi\phi}`. There are 8
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columns and the number of bins (rows) is :math:`R_\text{max}/b`, where
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:math:`b` is the specified bin width.
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This array can be output with :doc:`fix ave/time <fix_ave_time>`,
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.. code-block:: LAMMPS
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compute p all stress/spherical 0 0 0 0.1 10
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fix 2 all ave/time 100 1 100 c_p[*] file dump_p.out mode vector
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The values calculated by this compute are "intensive". The stress
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values will be in pressure :doc:`units <units>`. The number density
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values are in inverse volume :doc:`units <units>`.
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NOTE 1: The local stress does not include any Lennard-Jones tail
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corrections to the stress added by the
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:doc:`pair_modify tail yes <pair_modify>`
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command, since those are contributions to the global system pressure.
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Restrictions
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""""""""""""
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These computes calculate the stress tensor contributions for pair styles
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only (i.e., no bond, angle, dihedral, etc. contributions, and in the
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presence of bonded interactions, the result may be incorrect due to
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exclusions for :doc:`special bonds <special_bonds>` excluding pairs of atoms
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completely). It requires pairwise force calculations not available for most
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many-body pair styles. Note that :math:`k`-space calculations are also excluded.
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These computes are part of the EXTRA-COMPUTE package. They are only
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enabled if LAMMPS was built with that package. See the :doc:`Build
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package <Build_package>` doc page for more info.
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Related commands
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""""""""""""""""
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:doc:`compute stress/atom <compute_stress_atom>`, :doc:`compute pressure <compute_pressure>`,
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:doc:`compute stress/mop/profile <compute_stress_mop>`, :doc:`compute stress/cartesian <compute_stress_cartesian>`
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Default
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"""""""
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The keyword default for ke in style *stress/cylinder* is yes.
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----------
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.. _Ikeshoji4:
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**(Ikeshoji)** Ikeshoji, Hafskjold, Furuholt, Mol Sim, 29, 101-109, (2003).
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.. _Addington1:
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**(Addington)** Addington, Long, Gubbins, J Chem Phys, 149, 084109 (2018).
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