220 lines
10 KiB
ReStructuredText
220 lines
10 KiB
ReStructuredText
.. index:: pair_style mesont/tpm
|
|
|
|
pair_style mesont/tpm command
|
|
=============================
|
|
|
|
Syntax
|
|
""""""
|
|
|
|
|
|
.. parsed-literal::
|
|
|
|
pair_style mesont/tpm cut table_path BendingMode TPMType
|
|
|
|
* cut = the cutoff distance
|
|
* table_path = the path to the potential table
|
|
* BendingMode = the parameter defining the type of the bending potential for nanotubes: 0 - harmonic bending :ref:`(Srivastava) <Srivastava>`, 1 - anharmonic potential of bending and bending-buckling :ref:`(Zhigilei1) <Zhigilei1>`
|
|
* TPMType = the parameter determining the type of the inter-tube interaction term: 0 - segment-segment approach, 1 - segment-chain approach :ref:`(Zhigilei2 <Zhigilei2>`, :ref:`Zhigilei3) <Zhigilei3>`
|
|
|
|
The segment-segment approach is approximately 5 times slower than segment-chain approximation.
|
|
The parameter BendingMode also affects the calculation of the inter-tube interaction term when TPMType = 1. In this case, when BendingMode = 1, each continuous chain of segments is additionally replaced by a number of sub-chains divided by bending buckling kinks.
|
|
|
|
Examples
|
|
""""""""
|
|
|
|
|
|
.. parsed-literal::
|
|
|
|
pair_style mesont/tpm 30.0 MESONT-TABTP_10_10.xrs 0 0
|
|
|
|
Description
|
|
"""""""""""
|
|
|
|
The tubular potential model (TPM) force field is designed for mesoscopic
|
|
simulations of interacting flexible nanotubes. The force field is based on the
|
|
mesoscopic computational model suggested in Ref. :ref:`(Srivastava) <Srivastava>`.
|
|
In this model, each nanotube is represented by a chain of mesoscopic elements
|
|
in the form of stretchable cylindrical segments, where each segment consists
|
|
of multiple atoms. Each nanotube is divided into segments by a sequence of
|
|
nodes placed on the nanotube centerline. This sequence of nodes determines the
|
|
spatial position of the cylindrical segments and defines the configuration of
|
|
the entire tube.
|
|
|
|
The potential force field that controls the dynamic behavior of a system of
|
|
interacting nanotubes is given by the following equation defining the potential
|
|
energy of the system:
|
|
|
|
.. math::
|
|
|
|
U = U_{str} + U_{bnd} + U_{vdW}
|
|
|
|
where :math:`U_{str}` is the harmonic potential describing the stretching of nanotube
|
|
:ref:`(Srivastava) <Srivastava>`, :math:`U_{bnd}` is the potential for nanotube bending
|
|
:ref:`(Srivastava) <Srivastava>` and bending-buckling :ref:`(Zhigilei1) <Zhigilei1>`, and
|
|
:math:`U_{vdW}` is the potential describing van-der Waals interaction between nanotubes
|
|
:ref:`(Zhigilei2 <Zhigilei2>`, :ref:`Zhigilei3) <Zhigilei3>`. The stretching energy, :math:`U_{str}` ,
|
|
is given by the sum of stretching energies of individual nanotube segments.
|
|
The bending energy, :math:`U_{bnd}` , is given by the sum of bending energies in all
|
|
internal nanotube nodes. The tube-tube interaction energy, :math:`U_{vdW}` , is calculated
|
|
based on the tubular potential method suggested in Ref. :ref:`(Zhigilei2) <Zhigilei2>`.
|
|
The tubular potential method is briefly described below.
|
|
|
|
The interaction between two straight nanotubes of arbitrary length and
|
|
orientation is described by the approximate tubular potential developed in
|
|
:ref:`(Zhigilei3) <Zhigilei3>`. This potential approximates the results of direct
|
|
integration of carbon-carbon interatomic potential over the surfaces of the
|
|
interacting nanotubes, with the force sources homogeneously distributed over
|
|
the nanotube surfaces. The input data for calculation of tubular potentials
|
|
are partially tabulated. For single-walled CNTs of arbitrary chirality, the
|
|
tabulated potential data can be generated in the form of ASCII files
|
|
TPMSSTP.xrs and TPMA.xrs by the stand-alone code TMDPotGen included in the
|
|
tool directory of LAMMPS release. The potential provided with LAMMPS release,
|
|
MESONT-TABTP_10_10.xrs, is tabulated for (10,10) nanotubes.
|
|
|
|
Calculations of the interaction between curved or bent nanotubes are performed
|
|
on either segment-segment or segment-chain basis. In the first case, activated
|
|
when parameter TPMType is equal to 0, the tubular potential is calculated for
|
|
each pair of interacting mesoscopic segments. In this case, however, small
|
|
potential barriers for inter-tube sliding are introduced. While relatively
|
|
small, these barriers are still larger than the ones that originate from the
|
|
atomic-scale corrugation in atomistic modeling of inter-tube interaction. The
|
|
latter are too weak to prevent room-temperature rearrangements of defect-free
|
|
CNT, while the artificial mesoscopic barriers due to the segment-segment
|
|
interaction can impede sliding of nanotubes with respect to each other and
|
|
affect the kinetics of structural rearrangements in a system of nanotubes at
|
|
moderate mesoscopic temperatures. In the second case, activated when parameter
|
|
TPMType is equal to 1, the inter-tube interaction term is calculated based on
|
|
the segment-chain approach. In this case, for each NT segment, the list of its
|
|
neighboring segments is divided into short continuous chains of segments
|
|
belonging to individual nanotubes. For each pair of a segment and a chain, the
|
|
curved chain is approximated by a straight equivalent nanotube based on the
|
|
weighted approach suggested in Ref. :ref:`(Zhigilei2) <Zhigilei2>`. Finally, the
|
|
interaction between the segment and straight equivalent chain is calculated
|
|
based on the tubular potential. In this case, and in the absence of bending
|
|
buckling (i.e., when parameter BendingMode is equal to 0), the tubular
|
|
potential method ensures the absence of corrugation of the effective inter-tube
|
|
interaction potential for curved nanotubes and eliminates any barriers for the
|
|
inter-tube sliding. As a result, the tubular potential method can describe the
|
|
spontaneous self-assembly of nanotubes into continuous networks of bundles
|
|
:ref:`(Zhigilei1 <Zhigilei1>`, :ref:`Zhigilei3) <Zhigilei3>`.
|
|
|
|
|
|
----------
|
|
|
|
|
|
The TMD force field has been used for generation of nanotube films, fibers,
|
|
and vertically aligned forests of nanotubes. Mesoscopic dynamic simulations
|
|
were used to prepare realistic structures of continuous networks of nanotube
|
|
bundles and to study their structural and mechanical properties
|
|
:ref:`(Zhigilei1 <Zhigilei1>`, :ref:`Zhigilei3 <Zhigilei3>`, :ref:`Zhigilei4 <Zhigilei4>`,
|
|
:ref:`Zhigilei5 <Zhigilei5>`, :ref:`Zhigilei6) <Zhigilei6>`. With
|
|
additional models for heat transfer, this force filed was also used to
|
|
study the thermal transport properties of carbon nanotube films
|
|
:ref:`(Zhigilei7 <Zhigilei7>`, :ref:`Zhigilei8 <Zhigilei8>`, :ref:`Zhigilei8) <Zhigilei8>`.
|
|
The methods for modeling of
|
|
the mechanical energy dissipation into heat (energy exchange between the
|
|
dynamic degrees of freedom of the mesoscopic model and the energy of atomic
|
|
vibrations that are not explicitly represented in the model)
|
|
:ref:`(Zhigilei10) <Zhigilei10>` and mesoscopic description of covalent cross-links
|
|
between nanotubes :ref:`(Banna) <Banna>` have also been developed but are not
|
|
included in this first release of the LAMMPS implementation of the force field.
|
|
Further details can be found in references provided below.
|
|
|
|
The MESONT package also provides TMDGen code designed to generate initial samples
|
|
composed of straight and dispersed nanotubes of given chirality and length at a
|
|
given material density, which is available in tools directory. In the generated
|
|
samples, nanotubes are distributed with random positions and orientations. Both
|
|
periodic and free boundary conditions are available along each axis of the
|
|
system of coordinates. All parameters in the sample files generated with TMDGen
|
|
are given in metal :doc:`units <units>`.
|
|
|
|
Restrictions
|
|
""""""""""""
|
|
|
|
|
|
This pair style is a part of the USER-MSEONT package, and it is only enabled if
|
|
LAMMPS is built with that package. See the :doc:`Build package <Build_package>`
|
|
doc page for more information.
|
|
|
|
This pair potential requires use of :doc:`mesont atomic style <atom_style>`.
|
|
|
|
This pair potential requires the :doc:`newton <newton>` setting to be "on" for
|
|
pair interactions.
|
|
|
|
The cutoff distance should be set to be at least :math:`max\left[2L,\sqrt{L^2/2+(2R+T_{cut})^2}\right]` ,
|
|
where L is the maximum segment length, R is the maximum tube radius, and
|
|
:math:`T_{cut}` = 10.2 A is the maximum distance between the surfaces of interacting
|
|
segments. Because of the use of extended chain concept at CNT ends, the recommended
|
|
cutoff is 3L.
|
|
|
|
.. note::
|
|
|
|
Because of their size, *mesont* style potential files
|
|
are not bundled with LAMMPS. When compiling LAMMPS from
|
|
source code, the file ``TABTP_10_10.mesont`` should be downloaded
|
|
transparently from `https://download.lammps.org/potentials/TABTP_10_10.mesont <https://download.lammps.org/potentials/TABTP_10_10.mesont>`_
|
|
|
|
The ``TABTP_10_10.mesont`` potential file is parameterized for metal :doc:`units <units>`.
|
|
You can use the carbon nanotube mesoscopic force field with any LAMMPS units,
|
|
but you would need to create your own potential files with coefficients listed in
|
|
appropriate units, if your simulation does not use "metal" units.
|
|
|
|
The chirality parameters set during system generation must match the values
|
|
specified during generation of the potential tables.
|
|
|
|
Related commands
|
|
""""""""""""""""
|
|
|
|
:doc:`pair_coeff <pair_coeff>`
|
|
|
|
----------
|
|
|
|
.. _Srivastava:
|
|
|
|
**(Srivastava)** Zhigilei, Wei, Srivastava, Phys. Rev. B 71, 165417 (2005).
|
|
|
|
.. _Zhigilei1:
|
|
|
|
**(Zhigilei1)** Volkov and Zhigilei, ACS Nano 4, 6187 (2010).
|
|
|
|
.. _Zhigilei2:
|
|
|
|
**(Zhigilei2)** Volkov, Simov, Zhigilei, ASME paper IMECE2008, 68021 (2008).
|
|
|
|
.. _Zhigilei3:
|
|
|
|
**(Zhigilei3)** Volkov, Zhigilei, J. Phys. Chem. C 114, 5513 (2010).
|
|
|
|
.. _Zhigilei4:
|
|
|
|
**(Zhigilei4)** Wittmaack, Banna, Volkov, Zhigilei, Carbon 130, 69 (2018).
|
|
|
|
.. _Zhigilei5:
|
|
|
|
**(Zhigilei5)** Wittmaack, Volkov, Zhigilei, Compos. Sci. Technol. 166, 66 (2018).
|
|
|
|
.. _Zhigilei6:
|
|
|
|
**(Zhigilei6)** Wittmaack, Volkov, Zhigilei, Carbon 143, 587 (2019).
|
|
|
|
.. _Zhigilei7:
|
|
|
|
**(Zhigilei7)** Volkov, Zhigilei, Phys. Rev. Lett. 104, 215902 (2010).
|
|
|
|
.. _Zhigilei8:
|
|
|
|
**(Zhigilei8)** Volkov, Shiga, Nicholson, Shiomi, Zhigilei, J. Appl. Phys. 111, 053501 (2012).
|
|
|
|
.. _Zhigilei9:
|
|
|
|
**(Zhigilei9)** Volkov, Zhigilei, Appl. Phys. Lett. 101, 043113 (2012).
|
|
|
|
.. _Zhigilei10:
|
|
|
|
**(Zhigilei10)** Jacobs, Nicholson, Zemer, Volkov, Zhigilei, Phys. Rev. B 86, 165414 (2012).
|
|
|
|
.. _Banna:
|
|
|
|
**(Banna)** Volkov, Banna, Comp. Mater. Sci. 176, 109410 (2020).
|
|
|