39ea6ef30e
use the (newly redefined) \AA macro for Angstrom symbol throughout
instead of either \mathring{A} or AA
144 lines
4.6 KiB
ReStructuredText
144 lines
4.6 KiB
ReStructuredText
.. index:: pair_style zbl
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.. index:: pair_style zbl/gpu
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.. index:: pair_style zbl/kk
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.. index:: pair_style zbl/omp
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pair_style zbl command
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======================
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Accelerator Variants: *zbl/gpu*, *zbl/kk*, *zbl/omp*
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Syntax
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""""""
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.. code-block:: LAMMPS
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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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.. code-block:: LAMMPS
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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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.. math::
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E^{ZBL}_{ij} & = \frac{1}{4\pi\epsilon_0} \frac{Z_i Z_j \,e^2}{r_{ij}} \phi(r_{ij}/a)+ S(r_{ij})\\
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a & = \frac{0.46850}{Z_{i}^{0.23} + Z_{j}^{0.23}}\\
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\phi(x) & = 0.18175e^{-3.19980x} + 0.50986e^{-0.94229x} + 0.28022e^{-0.40290x} + 0.02817e^{-0.20162x}\\
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where *e* is the electron charge, :math:`\epsilon_0` is the electrical
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permittivity of vacuum, and :math:`Z_i` and :math:`Z_j` are the nuclear
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charges of the
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two atoms. The switching function :math:`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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* :math:`Z_i` (atomic number for first atom type, e.g. 13.0 for aluminum)
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* :math:`Z_j` (ditto for second atom type)
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The values of :math:`Z_i` and :math:`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 :math:`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 :math:`i==i` it is required that :math:`Z_i == Z_j`.
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When used with :doc:`hybrid/overlay <pair_hybrid>` and pairs are
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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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.. include:: accel_styles.rst
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----------
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Mixing, shift, table, tail correction, restart, rRESPA info
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"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
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For atom type pairs *i,j* and :math:`i \neq i`, the :math:`Z_i` and
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:math:`Z_j` coefficients
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can be mixed by taking :math:`Z_i` and :math:`Z_j` from the values
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specified for
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:math:`i == i` and :math:`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
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"""""""
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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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