89 lines
3.1 KiB
ReStructuredText
89 lines
3.1 KiB
ReStructuredText
.. index:: compute pressure/cylinder
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compute pressure/cylinder command
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=================================
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Syntax
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""""""
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.. parsed-literal::
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compute ID group-ID pressure/cylinder zlo zhi Rmax bin_width
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* ID, group-ID are documented in :doc:`compute <compute>` command
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* pressure/cylinder = style name of this compute command
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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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Examples
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""""""""
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.. code-block:: LAMMPS
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compute 1 all pressure/cylinder -10.0 10.0 15.0 0.25
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Description
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"""""""""""
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Define a computation that calculates the pressure tensor of a system in
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cylindrical coordinates, as discussed in :ref:`(Addington) <Addington1>`.
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This is useful for systems with a single axis of rotational symmetry,
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such as cylindrical micelles or carbon nanotubes. The compute splits the
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system into radial, cylindrical-shell-type bins of width bin_width,
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centered at x=0,y=0, and calculates the radial (P_rhorho), azimuthal
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(P_phiphi), and axial (P_zz) components of the configurational pressure
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tensor. The local density is also calculated for each bin, so that the
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true pressure can be recovered as P_kin+P_conf=density\*k\*T+P_conf. The
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output is a global array with 5 columns; one each for bin radius, local
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number density, P_rhorho, P_phiphi, and P_zz. The number of rows is
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governed by the values of Rmax and bin_width. Pressure tensor values are
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output in pressure units.
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Output info
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"""""""""""
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This compute calculates a global array with 5 columns and Rmax/bin_width
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rows. The output columns are: R (distance units), number density (inverse
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volume units), configurational radial pressure (pressure units),
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configurational azimuthal pressure (pressure units), and configurational
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axial pressure (pressure units).
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The values calculated by this compute are
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"intensive". The pressure values will be in pressure
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:doc:`units <units>`. The number density values will be in
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inverse volume :doc:`units <units>`.
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Restrictions
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""""""""""""
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This compute currently calculates the pressure tensor contributions
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for pair styles only (i.e. no bond, angle, dihedral, etc. contributions
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and in the presence of bonded interactions, the result will be incorrect
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due to exclusions for special bonds) and requires pair-wise force
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calculations not available for most many-body pair styles. K-space
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calculations are also excluded. Note that this pressure compute outputs
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the configurational terms only; the kinetic contribution is not included
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and may be calculated from the number density output by P_kin=density\*k\*T.
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This compute is part of the USER-MISC package. It is only enabled
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if LAMMPS was built with that package. See the :doc:`Build package <Build_package>` doc page for more info.
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Related commands
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""""""""""""""""
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:doc:`compute temp <compute_temp>`, :doc:`compute stress/atom <compute_stress_atom>`,
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:doc:`thermo_style <thermo_style>`,
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Default
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"""""""
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none
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----------
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.. _Addington1:
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**(Addington)** Addington, Long, Gubbins, J Chem Phys, 149, 084109 (2018).
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