1.. index:: pair_style mesont/tpm 2 3pair_style mesont/tpm command 4============================= 5 6Syntax 7"""""" 8 9 10.. parsed-literal:: 11 12 pair_style mesont/tpm cut table_path BendingMode TPMType 13 14* cut = the cutoff distance 15* table_path = the path to the potential table 16* 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>` 17* 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>` 18 19The segment-segment approach is approximately 5 times slower than segment-chain approximation. 20The 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. 21 22Examples 23"""""""" 24 25 26.. parsed-literal:: 27 28 pair_style mesont/tpm 30.0 MESONT-TABTP_10_10.xrs 0 0 29 30Description 31""""""""""" 32 33The tubular potential model (TPM) force field is designed for mesoscopic 34simulations of interacting flexible nanotubes. The force field is based on the 35mesoscopic computational model suggested in Ref. :ref:`(Srivastava) <Srivastava>`. 36In this model, each nanotube is represented by a chain of mesoscopic elements 37in the form of stretchable cylindrical segments, where each segment consists 38of multiple atoms. Each nanotube is divided into segments by a sequence of 39nodes placed on the nanotube centerline. This sequence of nodes determines the 40spatial position of the cylindrical segments and defines the configuration of 41the entire tube. 42 43The potential force field that controls the dynamic behavior of a system of 44interacting nanotubes is given by the following equation defining the potential 45energy of the system: 46 47.. math:: 48 49 U = U_{str} + U_{bnd} + U_{vdW} 50 51where :math:`U_{str}` is the harmonic potential describing the stretching of nanotube 52:ref:`(Srivastava) <Srivastava>`, :math:`U_{bnd}` is the potential for nanotube bending 53:ref:`(Srivastava) <Srivastava>` and bending-buckling :ref:`(Zhigilei1) <Zhigilei1>`, and 54:math:`U_{vdW}` is the potential describing van-der Waals interaction between nanotubes 55:ref:`(Zhigilei2 <Zhigilei2>`, :ref:`Zhigilei3) <Zhigilei3>`. The stretching energy, :math:`U_{str}` , 56is given by the sum of stretching energies of individual nanotube segments. 57The bending energy, :math:`U_{bnd}` , is given by the sum of bending energies in all 58internal nanotube nodes. The tube-tube interaction energy, :math:`U_{vdW}` , is calculated 59based on the tubular potential method suggested in Ref. :ref:`(Zhigilei2) <Zhigilei2>`. 60The tubular potential method is briefly described below. 61 62The interaction between two straight nanotubes of arbitrary length and 63orientation is described by the approximate tubular potential developed in 64:ref:`(Zhigilei3) <Zhigilei3>`. This potential approximates the results of direct 65integration of carbon-carbon interatomic potential over the surfaces of the 66interacting nanotubes, with the force sources homogeneously distributed over 67the nanotube surfaces. The input data for calculation of tubular potentials 68are partially tabulated. For single-walled CNTs of arbitrary chirality, the 69tabulated potential data can be generated in the form of ASCII files 70TPMSSTP.xrs and TPMA.xrs by the stand-alone code TMDPotGen included in the 71tool directory of LAMMPS release. The potential provided with LAMMPS release, 72MESONT-TABTP_10_10.xrs, is tabulated for (10,10) nanotubes. 73 74Calculations of the interaction between curved or bent nanotubes are performed 75on either segment-segment or segment-chain basis. In the first case, activated 76when parameter TPMType is equal to 0, the tubular potential is calculated for 77each pair of interacting mesoscopic segments. In this case, however, small 78potential barriers for inter-tube sliding are introduced. While relatively 79small, these barriers are still larger than the ones that originate from the 80atomic-scale corrugation in atomistic modeling of inter-tube interaction. The 81latter are too weak to prevent room-temperature rearrangements of defect-free 82CNT, while the artificial mesoscopic barriers due to the segment-segment 83interaction can impede sliding of nanotubes with respect to each other and 84affect the kinetics of structural rearrangements in a system of nanotubes at 85moderate mesoscopic temperatures. In the second case, activated when parameter 86TPMType is equal to 1, the inter-tube interaction term is calculated based on 87the segment-chain approach. In this case, for each NT segment, the list of its 88neighboring segments is divided into short continuous chains of segments 89belonging to individual nanotubes. For each pair of a segment and a chain, the 90curved chain is approximated by a straight equivalent nanotube based on the 91weighted approach suggested in Ref. :ref:`(Zhigilei2) <Zhigilei2>`. Finally, the 92interaction between the segment and straight equivalent chain is calculated 93based on the tubular potential. In this case, and in the absence of bending 94buckling (i.e., when parameter BendingMode is equal to 0), the tubular 95potential method ensures the absence of corrugation of the effective inter-tube 96interaction potential for curved nanotubes and eliminates any barriers for the 97inter-tube sliding. As a result, the tubular potential method can describe the 98spontaneous self-assembly of nanotubes into continuous networks of bundles 99:ref:`(Zhigilei1 <Zhigilei1>`, :ref:`Zhigilei3) <Zhigilei3>`. 100 101 102---------- 103 104 105The TMD force field has been used for generation of nanotube films, fibers, 106and vertically aligned forests of nanotubes. Mesoscopic dynamic simulations 107were used to prepare realistic structures of continuous networks of nanotube 108bundles and to study their structural and mechanical properties 109:ref:`(Zhigilei1 <Zhigilei1>`, :ref:`Zhigilei3 <Zhigilei3>`, :ref:`Zhigilei4 <Zhigilei4>`, 110:ref:`Zhigilei5 <Zhigilei5>`, :ref:`Zhigilei6) <Zhigilei6>`. With 111additional models for heat transfer, this force filed was also used to 112study the thermal transport properties of carbon nanotube films 113:ref:`(Zhigilei7 <Zhigilei7>`, :ref:`Zhigilei8 <Zhigilei8>`, :ref:`Zhigilei8) <Zhigilei8>`. 114The methods for modeling of 115the mechanical energy dissipation into heat (energy exchange between the 116dynamic degrees of freedom of the mesoscopic model and the energy of atomic 117vibrations that are not explicitly represented in the model) 118:ref:`(Zhigilei10) <Zhigilei10>` and mesoscopic description of covalent cross-links 119between nanotubes :ref:`(Banna) <Banna>` have also been developed but are not 120included in this first release of the LAMMPS implementation of the force field. 121Further details can be found in references provided below. 122 123The MESONT package also provides TMDGen code designed to generate initial samples 124composed of straight and dispersed nanotubes of given chirality and length at a 125given material density, which is available in tools directory. In the generated 126samples, nanotubes are distributed with random positions and orientations. Both 127periodic and free boundary conditions are available along each axis of the 128system of coordinates. All parameters in the sample files generated with TMDGen 129are given in metal :doc:`units <units>`. 130 131Restrictions 132"""""""""""" 133 134 135This pair style is a part of the MSEONT package, and it is only enabled if 136LAMMPS is built with that package. See the :doc:`Build package <Build_package>` 137doc page for more information. 138 139This pair potential requires use of :doc:`mesont atomic style <atom_style>`. 140 141This pair potential requires the :doc:`newton <newton>` setting to be "on" for 142pair interactions. 143 144The cutoff distance should be set to be at least :math:`max\left[2L,\sqrt{L^2/2+(2R+T_{cut})^2}\right]` , 145where L is the maximum segment length, R is the maximum tube radius, and 146:math:`T_{cut}` = 10.2 A is the maximum distance between the surfaces of interacting 147segments. Because of the use of extended chain concept at CNT ends, the recommended 148cutoff is 3L. 149 150.. note:: 151 152 Because of their size, *mesont* style potential files 153 are not bundled with LAMMPS. When compiling LAMMPS from 154 source code, the file ``TABTP_10_10.mesont`` should be downloaded 155 transparently from `https://download.lammps.org/potentials/TABTP_10_10.mesont <https://download.lammps.org/potentials/TABTP_10_10.mesont>`_ 156 157The ``TABTP_10_10.mesont`` potential file is parameterized for metal :doc:`units <units>`. 158You can use the carbon nanotube mesoscopic force field with any LAMMPS units, 159but you would need to create your own potential files with coefficients listed in 160appropriate units, if your simulation does not use "metal" units. 161 162The chirality parameters set during system generation must match the values 163specified during generation of the potential tables. 164 165Related commands 166"""""""""""""""" 167 168:doc:`pair_coeff <pair_coeff>` 169 170---------- 171 172.. _Srivastava: 173 174**(Srivastava)** Zhigilei, Wei, Srivastava, Phys. Rev. B 71, 165417 (2005). 175 176.. _Zhigilei1: 177 178**(Zhigilei1)** Volkov and Zhigilei, ACS Nano 4, 6187 (2010). 179 180.. _Zhigilei2: 181 182**(Zhigilei2)** Volkov, Simov, Zhigilei, ASME paper IMECE2008, 68021 (2008). 183 184.. _Zhigilei3: 185 186**(Zhigilei3)** Volkov, Zhigilei, J. Phys. Chem. C 114, 5513 (2010). 187 188.. _Zhigilei4: 189 190**(Zhigilei4)** Wittmaack, Banna, Volkov, Zhigilei, Carbon 130, 69 (2018). 191 192.. _Zhigilei5: 193 194**(Zhigilei5)** Wittmaack, Volkov, Zhigilei, Compos. Sci. Technol. 166, 66 (2018). 195 196.. _Zhigilei6: 197 198**(Zhigilei6)** Wittmaack, Volkov, Zhigilei, Carbon 143, 587 (2019). 199 200.. _Zhigilei7: 201 202**(Zhigilei7)** Volkov, Zhigilei, Phys. Rev. Lett. 104, 215902 (2010). 203 204.. _Zhigilei8: 205 206**(Zhigilei8)** Volkov, Shiga, Nicholson, Shiomi, Zhigilei, J. Appl. Phys. 111, 053501 (2012). 207 208.. _Zhigilei9: 209 210**(Zhigilei9)** Volkov, Zhigilei, Appl. Phys. Lett. 101, 043113 (2012). 211 212.. _Zhigilei10: 213 214**(Zhigilei10)** Jacobs, Nicholson, Zemer, Volkov, Zhigilei, Phys. Rev. B 86, 165414 (2012). 215 216.. _Banna: 217 218**(Banna)** Volkov, Banna, Comp. Mater. Sci. 176, 109410 (2020). 219 220