forked from lijiext/lammps
129 lines
4.3 KiB
Plaintext
129 lines
4.3 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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pair_style lj/cubic command :h3
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pair_style lj/cubic/omp command :h3
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[Syntax:]
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pair_style lj/cubic :pre
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[Examples:]
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pair_style lj/cubic
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pair_coeff * * 1.0 0.8908987 :pre
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[Description:]
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The {lj/cubic} style computes a truncated LJ interaction potential whose
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energy and force are continuous everywhere.
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Inside the inflection point the interaction is identical to the
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standard 12/6 "Lennard-Jones"_pair_lj.html potential.
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The LJ function outside the inflection point is replaced
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with a cubic function of distance. The energy, force, and second
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derivative are continuous at the inflection point.
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The cubic coefficient A3 is chosen so
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that both energy and force go to zero at the cutoff distance.
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Outside the cutoff distance the energy and force are zero.
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:c,image(Eqs/pair_lj_cubic.jpg)
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The location of the inflection point rs is defined
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by the LJ diameter, rs/sigma = (26/7)^1/6. The cutoff distance
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is defined by rc/rs = 67/48 or rc/sigma = 1.737....
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The analytic expression for the
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the cubic coefficient
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A3*rmin^3/epsilon = 27.93... is given in the paper by
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Holian and Ravelo "(Holian)"_#Holian.
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This potential is commonly used to study the shock mechanics
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of FCC solids, as in Ravelo et al. "(Ravelo)"_#Ravelo.
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The following coefficients must be defined for each pair of atom
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types via the "pair_coeff"_pair_coeff.html command as in the example
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above, or in the data file or restart files read by the
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"read_data"_read_data.html or "read_restart"_read_restart.html
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commands, or by mixing as described below:
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epsilon (energy units)
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sigma (distance units) :ul
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Note that sigma is defined in the LJ formula as the zero-crossing
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distance for the potential, not as the energy minimum, which
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is located at rmin = 2^(1/6)*sigma. In the above example, sigma = 0.8908987,
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so rmin = 1.
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:line
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Styles with a {cuda}, {gpu}, {omp}, or {opt} suffix are functionally
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the same as the corresponding style without the suffix. They have
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been optimized to run faster, depending on your available hardware, as
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discussed in "Section_accelerate"_Section_accelerate.html of the
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manual. The accelerated styles take the same arguments and should
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produce the same results, except for round-off and precision issues.
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These accelerated styles are part of the USER-CUDA, GPU, USER-OMP and OPT
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packages, respectively. They are only enabled if LAMMPS was built with
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those packages. See the "Making LAMMPS"_Section_start.html#start_3
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section for more info.
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You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the "-suffix command-line
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switch"_Section_start.html#start_7 when you invoke LAMMPS, or you can
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use the "suffix"_suffix.html command in your input script.
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See "Section_accelerate"_Section_accelerate.html of the manual for
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more instructions on how to use the accelerated styles effectively.
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:line
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[Mixing, shift, table, tail correction, restart, rRESPA info]:
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For atom type pairs I,J and I != J, the epsilon and sigma coefficients
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and cutoff distance for all of the lj/cut pair styles can be mixed.
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The default mix value is {geometric}. See the "pair_modify" command
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for details.
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The lj/cubic pair style does not support the
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"pair_modify"_pair_modify.html shift option,
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since pair interaction is already smoothed to 0.0 at the
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cutoff.
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The "pair_modify"_pair_modify.html table option is not relevant
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for this pair style.
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The lj/cubic pair style does not support the
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"pair_modify"_pair_modify.html tail option for adding long-range tail
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corrections to energy and pressure, since there are no corrections for
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a potential that goes to 0.0 at the cutoff.
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The lj/cubic pair style writes its information to "binary
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restart files"_restart.html, so pair_style and pair_coeff commands do
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not need to be specified in an input script that reads a restart file.
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The lj/cubic pair style can only be used via the {pair}
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keyword of the "run_style respa"_run_style.html command. It does not
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support the {inner}, {middle}, {outer} keywords.
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:line
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[Restrictions:] none
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[Related commands:]
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"pair_coeff"_pair_coeff.html
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[Default:] none
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:line
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:link(Holian)
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[(Holian)] Holian and Ravelo, Phys Rev B, 51, 11275 (1995).
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:link(Ravelo)
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[(Ravelo)] Ravelo, Holian, Germann and Lomdahl, Phys Rev B, 70, 014103 (2004).
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