forked from lijiext/lammps
166 lines
5.2 KiB
Plaintext
166 lines
5.2 KiB
Plaintext
.. index:: pair_style zbl
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pair_style zbl command
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======================
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pair_style zbl/gpu command
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==========================
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pair_style zbl/omp command
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==========================
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Syntax
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""""""
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.. parsed-literal::
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pair_style zbl inner outer
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* inner = distance where switching function begins
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* outer = global cutoff for ZBL interaction
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Examples
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""""""""
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.. parsed-literal::
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pair_style zbl 3.0 4.0
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pair_coeff * * 73.0 73.0
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pair_coeff 1 1 14.0 14.0
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Description
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"""""""""""
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Style *zbl* computes the Ziegler-Biersack-Littmark (ZBL) screened nuclear
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repulsion for describing high-energy collisions between atoms.
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:ref:`(Ziegler) <Ziegler>`. It includes an additional switching function
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that ramps the energy, force, and curvature smoothly to zero
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between an inner and outer cutoff. The potential
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energy due to a pair of atoms at a distance r_ij is given by:
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.. image:: Eqs/pair_zbl.jpg
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:align: center
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where e is the electron charge, epsilon_0 is the electrical
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permittivity of vacuum, and Z_i and Z_j are the nuclear charges of the
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two atoms. The switching function S(r) is identical to that used by
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:doc:`pair_style lj/gromacs <pair_gromacs>`. Here, the inner and outer
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cutoff are the same for all pairs of atom types.
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The following coefficients must be defined for each pair of atom types
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via the :doc:`pair_coeff <pair_coeff>` command as in the examples above,
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or in the LAMMPS data file.
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* Z_i (atomic number for first atom type, e.g. 13.0 for aluminum)
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* Z_j (ditto for second atom type)
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The values of Z_i and Z_j are normally equal to the atomic
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numbers of the two atom types. Thus, the user may optionally
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specify only the coefficients for each I==I pair, and rely
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on the obvious mixing rule for cross interactions (see below).
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Note that when I==I it is required that Z_i == Z_j. When used
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with :doc:`hybrid/overlay <pair_hybrid>` and pairs are assigned
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to more than one sub-style, the mixing rule is not used and
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each pair of types interacting with the ZBL sub-style must
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be included in a pair_coeff command.
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.. note::
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The numerical values of the exponential decay constants in the
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screening function depend on the unit of distance. In the above
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equation they are given for units of angstroms. LAMMPS will
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automatically convert these values to the distance unit of the
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specified LAMMPS :doc:`units <units>` setting. The values of Z should
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always be given as multiples of a proton's charge, e.g. 29.0 for
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copper.
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----------
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Styles with a *gpu*\ , *intel*\ , *kk*\ , *omp*\ , or *opt* suffix are
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functionally the same as the corresponding style without the suffix.
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They have been optimized to run faster, depending on your available
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hardware, as discussed in :doc:`Section_accelerate <Section_accelerate>`
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of the manual. The accelerated styles take the same arguments and
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should produce the same results, except for round-off and precision
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issues.
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These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
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USER-OMP and OPT packages, respectively. They are only enabled if
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LAMMPS was built with those packages. See the :ref:`Making LAMMPS <start_3>` section for more info.
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You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the :ref:`-suffix command-line switch <start_7>` when you invoke LAMMPS, or you can
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use the :doc:`suffix <suffix>` command in your input script.
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See :doc:`Section_accelerate <Section_accelerate>` of the manual for
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more instructions on how to use the accelerated styles effectively.
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----------
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**Mixing, shift, table, tail correction, restart, rRESPA info**\ :
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For atom type pairs I,J and I != J, the Z_i and Z_j coefficients
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can be mixed by taking Z_i and Z_j from the values specified for
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I == I and J == J cases. When used
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with :doc:`hybrid/overlay <pair_hybrid>` and pairs are assigned
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to more than one sub-style, the mixing rule is not used and
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each pair of types interacting with the ZBL sub-style
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must be included in a pair_coeff command.
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The :doc:`pair_modify <pair_modify>` mix option has no effect on
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the mixing behavior
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The ZBL pair style does not support the :doc:`pair_modify <pair_modify>`
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shift option, since the ZBL interaction is already smoothed to 0.0 at
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the cutoff.
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The :doc:`pair_modify <pair_modify>` table option is not relevant for
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this pair style.
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This pair style does not support the :doc:`pair_modify <pair_modify>`
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tail option for adding long-range tail corrections to energy and
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pressure, since there are no corrections for a potential that goes to
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0.0 at the cutoff.
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This pair style does not write information to :doc:`binary restart files <restart>`, so pair_style and pair_coeff commands must be
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specified in an input script that reads a restart file.
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This pair style can only be used via the *pair* keyword of the
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:doc:`run_style respa <run_style>` command. It does not support the
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*inner*\ , *middle*\ , *outer* keywords.
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----------
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Restrictions
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""""""""""""
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none
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Related commands
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""""""""""""""""
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:doc:`pair_coeff <pair_coeff>`
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**Default:** none
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----------
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.. _Ziegler:
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**(Ziegler)** J.F. Ziegler, J. P. Biersack and U. Littmark, "The
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Stopping and Range of Ions in Matter," Volume 1, Pergamon, 1985.
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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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