151 lines
5.7 KiB
ReStructuredText
151 lines
5.7 KiB
ReStructuredText
.. index:: pair_style drip
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pair_style drip 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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pair_style hybrid/overlay drip [styles ...]
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* styles = other styles to be overlayed with drip (optional)
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Examples
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""""""""
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.. code-block:: LAMMPS
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pair_style hybrid/overlay drip
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pair_coeff * * none
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pair_coeff * * drip C.drip C
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pair_style hybrid/overlay drip rebo
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pair_coeff * * drip C.drip C
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pair_coeff * * rebo CH.airebo C
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pair_style hybrid/overlay drip rebo
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pair_coeff * * drip C.drip C NULL
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pair_coeff * * rebo CH.airebo C H
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Description
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"""""""""""
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Style *drip* computes the interlayer interactions of layered materials using
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the dihedral-angle-corrected registry-dependent (DRIP) potential as described
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in :ref:`(Wen) <Wen2018>`, which is based on the :ref:`(Kolmogorov) <Kolmogorov2005>`
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potential and provides an improved prediction for forces.
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The total potential energy of a system is
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.. math::
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E = & \frac{1}{2} \sum_{i} \sum_{j\notin\text{layer}\,i} \phi_{ij} \\
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\phi_{ij} = &f_\text{c}(x_r) \left[ e^{-\lambda(r_{ij} - z_0 )} \left[C+f(\rho_{ij})+ g(\rho_{ij}, \{\alpha_{ij}^{(m)}\}) \right]- A\left (\frac{z_0}{r_{ij}} \right)^6 \right]
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where the :math:`r^{-6}` term models the attractive London dispersion,
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the exponential term is designed to capture the registry effect due to
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overlapping *pi* bonds, and *fc* is a cutoff function.
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This potential (DRIP) only provides the interlayer interactions between
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graphene layers. So, to perform a realistic simulation, it should be used in
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combination with an intralayer potential such as :doc:`REBO <pair_airebo>` and
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:doc:`Tersoff <pair_tersoff>`.
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To keep the intralayer interactions unaffected, we should avoid applying DRIP
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to contribute energy to intralayer interactions. This can be achieved by
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assigning different molecular IDs to atoms in different layers, and DRIP is
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implemented such that only atoms with different molecular ID can interact with
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each other. For this purpose, :doc:`atom style <atom_style>` "molecular" or
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"full" has to be used.
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On the other way around, :doc:`REBO <pair_airebo>` (:doc:`Tersoff <pair_tersoff>`
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or any other potential used to provide the intralayer interactions) should not
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interfere with the interlayer interactions described by DRIP. This is typically
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automatically achieved using the commands provided in the *Examples* section
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above, since the cutoff distance for carbon-carbon interaction in the intralayer
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potentials (e.g. 2 Angstrom for :doc:`REBO <pair_airebo>`) is much smaller than
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the equilibrium layer distance of graphene layers (about 3.4 Angstrom).
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If you want, you can enforce this by assigning different atom types to atoms in
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different layers, and apply an intralayer potential to one atom type.
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See :doc:`pair_hybrid <pair_hybrid>` for details.
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----------
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The :doc:`pair_coeff <pair_coeff>` command for DRIP takes *4+N* arguments, where
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*N* is the number of LAMMPS atom types. The fist three arguments must be fixed
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to be *\* \* drip*, the fourth argument is the path to the DRIP parameter file,
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and the remaining N arguments specifying the mapping between element in the
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parameter file and atom types. For example, if your LAMMPS simulation has 3 atom
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types and you want all of them to be C, you would use the following pair_coeff
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command:
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.. code-block:: LAMMPS
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pair_coeff * * drip C.drip C C C
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If a mapping value is specified as NULL, the mapping is not performed. This
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could be useful when DRIP is used to model part of the system where other
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element exists. Suppose you have a hydrocarbon system, with C of atom type 1
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and H of atom type 2, you can use the following command to inform DRIP not to
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model H atoms:
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.. code-block:: LAMMPS
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pair_style hybrid/overlay drip rebo
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pair_coeff * * drip C.drip C NULL
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pair_coeff * * rebo CH.airebo C H
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.. note::
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The potential parameters developed in :ref:`(Wen) <Wen2018>` are provided with
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LAMMPS (see the "potentials" directory). Besides those in :ref:`Wen <Wen2018>`, an
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additional parameter "normal_cutoff", specific to the LAMMPS implementation, is
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used to find the three nearest neighbors of an atom to construct the normal.
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----------
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Mixing, shift, table, tail correction, restart, rRESPA info
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"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
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This pair style does not support the pair_modify mix, shift, table,
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and tail options.
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This pair style does not write their information to binary restart files, since
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it is stored in potential files. Thus, you need to re-specify the pair_style and
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pair_coeff commands in an input script that reads a restart file.
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Restrictions
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""""""""""""
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This pair style is part of the INTERLAYER package. It is only enabled if
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LAMMPS was built with that package. See the :doc:`Build package
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<Build_package>` page for more info.
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This pair style requires the :doc:`newton <newton>` setting to be "on" for
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pair interactions.
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The *C.drip* parameter file provided with LAMMPS (see the "potentials"
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directory) is parameterized for metal :doc:`units <units>`. You can use
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the DRIP potential with any LAMMPS units, but you would need to create
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your own custom parameter file with coefficients listed in the
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appropriate units, if your simulation does not use "metal" units.
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Related commands
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""""""""""""""""
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:doc:`pair_style lebedeva_z <pair_lebedeva_z>`,
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:doc:`pair_style kolmogorov/crespi/z <pair_kolmogorov_crespi_z>`,
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:doc:`pair_style kolmogorov/crespi/full <pair_kolmogorov_crespi_full>`,
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:doc:`pair_style ilp/graphene/hbn <pair_ilp_graphene_hbn>`.
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----------
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.. _Wen2018:
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**(Wen)** M. Wen, S. Carr, S. Fang, E. Kaxiras, and E. B. Tadmor, Phys. Rev. B,
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98, 235404 (2018)
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.. _Kolmogorov2005:
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**(Kolmogorov)** A. N. Kolmogorov, V. H. Crespi, Phys. Rev. B 71, 235415 (2005)
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