Shifted Tersoff Potential

doc/src/pair_tersoff_shift.rst

@@ -0,0 +1,116 @@
+.. index:: pair_style tersoff/shift
+
+Syntax
+""""""
+
+.. code-block:: LAMMPS
+
+   pair_style tersoff/shift delta
+
+* delta = the shift applied to the equilibrium bond length of the tersoff potential.
+
+Examples
+""""""""
+
+.. code-block:: LAMMPS
+
+   pair_style tersoff/shift delta
+   pair_coeff * * Si.tersoff Si
+   pair_coeff * * BNC.tersoff B N
+
+Description
+"""""""""""
+
+The *tersoff/shift* style computes the energy E of a system of atoms, whose formula
+is the same as a 3-body Tersoff potential :ref:`(Tersoff_1) <Tersoff_11>`. The only
+modification is that the original equilibrium bond length (:math: `r_0`) of the 
+system is shifted to :math:`r_0-\delta`.
+
+.. note::
+
+   The sign of :math:`\delta` determines whether the resulting equilibrium bond length will be elongated 
+   or shrinked relative to the original value. Specifically, values of :math:`\delta < 0` will result in 
+   elongation of the bond length, while values of :math:`\delta > 0` will result in shrinking of the bond length.
+
+This style is designed for simulations of closely matched van der Waals heterostructures. For instance, let's 
+consider the case of a system with few-layers graphene atop a thick hexagonal boron nitride (h-BN) substrate 
+simulated using periodic boundary conditions. The experimental lattice mismatch of ~1.8% between graphene and h-BN
+is not well captured by the equilibrium lattice constants of available potentials, thus a small in-plane strain
+will be introduced in the system when building a periodic supercell.To minimize the effect of strain on
+simulation results, the *tersoff/shift* style is proposed that allows adjusting the equilibrium bond length
+of one of the two materials (e.g., h-BN). Validitation, benchmark tests and applications of the *tersoff/shift* style
+can be found in :ref:`(Mandelli_1) <Mandelli1>` and :ref:`(Ouyang_1) <Ouyang5>`.
+
+For the specific case discussed above, the force field can be defined as
+
+.. code-block:: LAMMPS
+
+   pair_style  hybrid/overlay rebo tersoff/shift -4.07e-3 ilp/graphene/hbn 16.0 coul/shield 16.0
+   pair_coeff  * * rebo              CH.rebo     NULL NULL C
+   pair_coeff  * * tersoff/shift     BNC.tersoff B    N    NULL
+   pair_coeff  * * ilp/graphene/hbn  BNCH.ILP    B    N    C
+   pair_coeff  1 1 coul/shield 0.70
+   pair_coeff  1 2 coul/shield 0.695
+   pair_coeff  2 2 coul/shield 0.69
+
+Except for the shift, the usage of the *tersoff/shift* style is the same as that for the
+*tersoff* style :doc:`tersoff <pair_tersoff>`.
+
+
+Mixing, shift, table, tail correction, restart, rRESPA info
+"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+
+For atom type pairs I,J and I != J, where types I and J correspond to
+two different element types, mixing is performed by LAMMPS as
+described above from values in the potential file.
+
+This pair style does not support the :doc:`pair_modify <pair_modify>`
+shift, table, and tail options.
+
+This pair style does not write its information to :doc:`binary restart files <restart>`, since it is stored in potential files.  Thus, you
+need to re-specify the pair_style and pair_coeff commands in an input
+script that reads a restart file.
+
+This pair style can only be used via the *pair* keyword of the
+:doc:`run_style respa <run_style>` command.  It does not support the
+*inner*\ , *middle*\ , *outer* keywords.
+
+----------
+
+Restrictions
+""""""""""""
+
+This pair style is part of the USER-MISC package.  It is only enabled
+if LAMMPS was built with that package.  See the :doc:`Build package <Build_package>` doc page for more info.
+
+This pair style requires the :doc:`newton <newton>` setting to be "on"
+for pair interactions.
+
+The Tersoff potential files provided with LAMMPS (see the potentials
+directory) are parameterized for metal :doc:`units <units>`.  You can
+use the Tersoff potential with any LAMMPS units, but you would need to
+create your own Tersoff potential file with coefficients listed in the
+appropriate units if your simulation does not use "metal" units.
+
+Related commands
+""""""""""""""""
+
+:doc:`pair_coeff <pair_coeff>`,
+:doc:`pair_style tersoff <pair_tersoff>`,
+:doc:`pair_style ilp/graphene/hbn <pair_ilp_graphene_hbn>`.
+
+Default
+"""""""
+
+none
+
+----------
+
+.. _Mandelli1:
+
+**(Mandelli_1)** D. Mandelli, W. Ouyang, M. Urbakh, and O. Hod, ACS Nano 13(7), 7603-7609 (2019).
+
+
+.. _Ouyang5:
+
+**(Ouyang_1)** W. Ouyang et al., J. Chem. Theory Comput. 16(1), 666-676 (2020).