+Syntax: +
+pair_style airebo cutoff LJ_flag TORSION_flag ++
Examples: +
+pair_style airebo 3.0 +pair_style airebo 2.5 1 0 +pair_coeff * * ../potentials/CH.airebo H C ++
Description: +
+The airebo pair style computes the Adaptive Intermolecular Reactive +Empirical Bond Order (AIREBO) Potential of (Stuart) for a +system of carbon and/or hydrogen atoms. The potential +consists of three terms: +
+
+By default, all three terms are included. If the two optional flag +arguments to the pair_style command are included, the LJ and torsional +terms can be turned off. Note that both or neither of the flags must +be included. +
+The detailed formulas for this potential are given in +(Stuart); here we provide only a brief description. +
+The E_REBO term has the same functional form as the hydrocarbon REBO +potential developed in (Brenner). The coefficients for +E_REBO in AIREBO are essentially the same as Brenner's potential, but +a few fitted spline values are slightly different. For most cases the +E_REBO term in AIREBO will produce the same energies, forces and +statistical averages as the original REBO potential from which it was +derived. The E_REBO term in the AIREBO potential gives the model its +reactive capabilities and only describes short-ranged C-C, C-H and H-H +interactions (r < 2 Angstroms). These interactions have strong +coordination-dependence through a bond order parameter, which adjusts +the attraction between the I,J atoms based on the position of other +nearby atoms and thus has 3- and 4-body dependence. +
+The E_LJ term adds longer-ranged interactions (2 < r < cutoff) using a +form similar to the standard Lennard Jones potential. +The E_LJ term in AIREBO contains a series of switching functions so +that the short-ranged LJ repulsion (1/r^12) does not interfere with +the energetics captured by the E_REBO term. The extent of the E_LJ +interactions is determined by the cutoff argument to the pair_style +command which is a scale factor. For each type pair (C-C, C-H, H-H) +the cutoff is obtained by multiplying the scale factor by the sigma +value defined in the potential file for that type pair. In the +standard AIREBO potential, sigma_CC = 3.4 Angstroms, so with a scale +factor of 3.0 (the argument in pair_style), the resulting E_LJ cutoff +would be 10.2 Angstroms. +
+The E_TORSION term is an explicit 4-body potential that describes +various diheadral angle preferences in hydrocarbon configurations. +
+Only a single pair_coeff command is used with the airebo style which +specifies an AIREBO potential file with parameters for C and H. These +are mapped to LAMMPS atom types by specifying N additional arguments +after the filename in the pair_coeff command, where N is the number of +LAMMPS atom types: +
+As an example, if your LAMMPS simulation has 4 atoms types and you +want the 1st 3 to be C, and the 4th to be H, you would use the +following pair_coeff command: +
+pair_coeff * * CH.airebo C C C H ++
The 1st 2 arguments must be * * so as to span all LAMMPS atom types. +The first three C arguments map LAMMPS atom types 1,2,3 to the C +element in the AIREBO file. The final H argument maps LAMMPS atom +type 4 to the H element in the SW file. If a mapping value is +specified as NULL, the mapping is not performed. This can be used +when a airebo potential is used as part of the hybrid pair style. +The NULL values are placeholders for atom types that will be used with +other potentials. +
+The parameters/coefficients for the AIREBO potentials are listed in +the CH.airebo file to agree with the original (Stuart) +paper. Thus the parameters are specific to this potential and the way +it was fit, so modifying the file should be done cautiously. Also +note that the E_LJ and E_TORSION terms in AIREBO are intended to be +used with the E_REBO term and not as stand-alone potentials. Thus we +don't suggest you use pair_style airebo with the E_REBO term turned +off. +
+Mixing, shift, table, tail correction, per-atom energy/stress, and +restart info: +
+This pair style does not support the pair_modify +mix, shift, table, and tail options. +
+This pair style does not calculate per-atom energy and stress, as used +by the compute epair/atom, compute +stress/atom, and dump custom +commands. +
+This pair style does not write its information to binary restart +files, 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. +
+Restrictions: +
+This pair style is part of the "manybody" package. It is only enabled +if LAMMPS was built with that package (which it is by default). See +the Making LAMMPS section for more info. +
+This pair potential requires the newton setting to be +"on" for pair interactions. +
+The CH.airebo potential file provided with LAMMPS (see the potentials +directory) is parameterized for metal units. You can use +the AIREBO potential with any LAMMPS units, but you would need to +create your own AIREBO potential file with coefficients listed in the +appropriate units if your simulation doesn't use "metal" units. +
+Related commands: +
+ +Default: none +
+(Stuart) Stuart, Tutein, Harrison, J Chem Phys, 112, 6472-6486 +(2000). +
+ + +(Brenner) Brenner, Shenderova, Harrison, Stuart, Ni, Sinnott, J +Physics: Condensed Matter, 14, 783-802 (2002). +
+ diff --git a/doc/pair_airebo.txt b/doc/pair_airebo.txt new file mode 100644 index 0000000000..4ab19891e9 --- /dev/null +++ b/doc/pair_airebo.txt @@ -0,0 +1,151 @@ +"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c + +:link(lws,http://lammps.sandia.gov) +:link(ld,Manual.html) +:link(lc,Section_commands.html#comm) + +:line + +pair_style airebo command :h3 + +[Syntax:] + +pair_style airebo cutoff LJ_flag TORSION_flag :pre + +cutoff = LJ cutoff (sigma scale factor) +LJ_flag = 0/1 to turn off/on the LJ term in AIREBO (optional) +TORSION_flag = 0/1 to turn off/on the torsion term in AIREBO (optional) :ul + +[Examples:] + +pair_style airebo 3.0 +pair_style airebo 2.5 1 0 +pair_coeff * * ../potentials/CH.airebo H C :pre + +[Description:] + +The {airebo} pair style computes the Adaptive Intermolecular Reactive +Empirical Bond Order (AIREBO) Potential of "(Stuart)"_#Stuart for a +system of carbon and/or hydrogen atoms. The potential +consists of three terms: + +:c,image(Eqs/pair_airebo.jpg) + +By default, all three terms are included. If the two optional flag +arguments to the pair_style command are included, the LJ and torsional +terms can be turned off. Note that both or neither of the flags must +be included. + +The detailed formulas for this potential are given in +"(Stuart)"_#Stuart; here we provide only a brief description. + +The E_REBO term has the same functional form as the hydrocarbon REBO +potential developed in "(Brenner)"_#Brenner. The coefficients for +E_REBO in AIREBO are essentially the same as Brenner's potential, but +a few fitted spline values are slightly different. For most cases the +E_REBO term in AIREBO will produce the same energies, forces and +statistical averages as the original REBO potential from which it was +derived. The E_REBO term in the AIREBO potential gives the model its +reactive capabilities and only describes short-ranged C-C, C-H and H-H +interactions (r < 2 Angstroms). These interactions have strong +coordination-dependence through a bond order parameter, which adjusts +the attraction between the I,J atoms based on the position of other +nearby atoms and thus has 3- and 4-body dependence. + +The E_LJ term adds longer-ranged interactions (2 < r < cutoff) using a +form similar to the standard "Lennard Jones potential"_pair_lj.html. +The E_LJ term in AIREBO contains a series of switching functions so +that the short-ranged LJ repulsion (1/r^12) does not interfere with +the energetics captured by the E_REBO term. The extent of the E_LJ +interactions is determined by the {cutoff} argument to the pair_style +command which is a scale factor. For each type pair (C-C, C-H, H-H) +the cutoff is obtained by multiplying the scale factor by the sigma +value defined in the potential file for that type pair. In the +standard AIREBO potential, sigma_CC = 3.4 Angstroms, so with a scale +factor of 3.0 (the argument in pair_style), the resulting E_LJ cutoff +would be 10.2 Angstroms. + +The E_TORSION term is an explicit 4-body potential that describes +various diheadral angle preferences in hydrocarbon configurations. + +Only a single pair_coeff command is used with the {airebo} style which +specifies an AIREBO potential file with parameters for C and H. These +are mapped to LAMMPS atom types by specifying N additional arguments +after the filename in the pair_coeff command, where N is the number of +LAMMPS atom types: + +filename +N element names = mapping of AIREBO elements to atom types :ul + +As an example, if your LAMMPS simulation has 4 atoms types and you +want the 1st 3 to be C, and the 4th to be H, you would use the +following pair_coeff command: + +pair_coeff * * CH.airebo C C C H :pre + +The 1st 2 arguments must be * * so as to span all LAMMPS atom types. +The first three C arguments map LAMMPS atom types 1,2,3 to the C +element in the AIREBO file. The final H argument maps LAMMPS atom +type 4 to the H element in the SW file. If a mapping value is +specified as NULL, the mapping is not performed. This can be used +when a {airebo} potential is used as part of the {hybrid} pair style. +The NULL values are placeholders for atom types that will be used with +other potentials. + +The parameters/coefficients for the AIREBO potentials are listed in +the CH.airebo file to agree with the original "(Stuart)"_#Stuart +paper. Thus the parameters are specific to this potential and the way +it was fit, so modifying the file should be done cautiously. Also +note that the E_LJ and E_TORSION terms in AIREBO are intended to be +used with the E_REBO term and not as stand-alone potentials. Thus we +don't suggest you use pair_style airebo with the E_REBO term turned +off. + +:line + +[Mixing, shift, table, tail correction, per-atom energy/stress, and +restart info]: + +This pair style does not support the "pair_modify"_pair_modify.html +mix, shift, table, and tail options. + +This pair style does not calculate per-atom energy and stress, as used +by the "compute epair/atom"_compute_epair_atom.html, "compute +stress/atom"_compute_stress_atom.html, and "dump custom"_dump.html +commands. + +This pair style does not write its information to "binary restart +files"_restart.html, 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. + +[Restrictions:] + +This pair style is part of the "manybody" package. It is only enabled +if LAMMPS was built with that package (which it is by default). See +the "Making LAMMPS"_Section_start.html#2_3 section for more info. + +This pair potential requires the "newton"_newton.html setting to be +"on" for pair interactions. + +The CH.airebo potential file provided with LAMMPS (see the potentials +directory) is parameterized for metal "units"_units.html. You can use +the AIREBO potential with any LAMMPS units, but you would need to +create your own AIREBO potential file with coefficients listed in the +appropriate units if your simulation doesn't use "metal" units. + +[Related commands:] + +"pair_coeff"_pair_coeff.html + +[Default:] none + +:line + +:link(Stuart) +[(Stuart)] Stuart, Tutein, Harrison, J Chem Phys, 112, 6472-6486 +(2000). + +:link(Brenner) +[(Brenner)] Brenner, Shenderova, Harrison, Stuart, Ni, Sinnott, J +Physics: Condensed Matter, 14, 783-802 (2002).