"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)

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pair_style morse command :h3
pair_style morse/gpu command :h3
pair_style morse/omp command :h3
pair_style morse/opt command :h3
pair_style morse/smooth/linear command :h3
pair_style morse/smooth/linear/omp command :h3
pair_style morse/soft command :h3

[Syntax:]

pair_style style args :pre

style = {morse} or {morse/smooth/linear} or {morse/soft}
args = list of arguments for a particular style :ul
 {morse} args = cutoff
   cutoff = global cutoff for Morse interactions (distance units)
 {morse/smooth/linear} args = cutoff
   cutoff = global cutoff for Morse interactions (distance units)
 {morse/soft} args = n lf cutoff
   n = soft-core parameter
   lf      = transformation range is lf < lambda < 1
   cutoff  = global cutoff for Morse interactions (distance units)
:pre

[Examples:]

pair_style morse 2.5
pair_style morse/smooth/linear 2.5
pair_coeff * * 100.0 2.0 1.5
pair_coeff 1 1 100.0 2.0 1.5 3.0

pair_style morse/soft 4 0.9 10.0
pair_coeff * * 100.0 2.0 1.5 1.0
pair_coeff 1 1 100.0 2.0 1.5 1.0 3.0 :pre

[Description:]

Style {morse} computes pairwise interactions with the formula

:c,image(Eqs/pair_morse.jpg)

Rc is the cutoff.

The following coefficients must be defined for each pair of atoms
types via the "pair_coeff"_pair_coeff.html command as in the examples
above, or in the data file or restart files read by the
"read_data"_read_data.html or "read_restart"_read_restart.html
commands:

D0 (energy units)
alpha (1/distance units)
r0 (distance units)
cutoff (distance units) :ul

The last coefficient is optional.  If not specified, the global morse
cutoff is used.

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The {morse/smooth/linear} variant is similar to the lj/smooth/linear
variant in that it adds to the potential a shift and a linear term
so that both, potential energy and force, go to zero at the cut-off:

:c,image(Eqs/pair_morse_smooth_linear.jpg)

The syntax of the pair_style and pair_coeff commands are the same for
the {morse} and {morse/smooth/linear} styles.

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The {morse/soft} variant is similar to the {lj/cut/soft} pair style
in that it modifies the potential at short range to have a soft core.
This helps to avoid singularities during free energy calculation in
which sites are created or anihilated. The formula differs from that
of {lj/cut/soft}, and is instead given by:

:c,image(Eqs/pair_morse_soft.jpg)

The {morse/soft} style requires the following pair coefficients:

D0 (energy units)
alpha (1/distance units)
r0 (distance units)
lamda (unitless, between 0.0 and 1.0)
cutoff (distance units) :ul

The last coefficient is optional.  If not specified, the global morse
cutoff is used.

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Styles with a {gpu}, {intel}, {kk}, {omp}, or {opt} suffix are
functionally the same as the corresponding style without the suffix.
They have been optimized to run faster, depending on your available
hardware, as discussed in "Section 5"_Section_accelerate.html
of the manual.  The accelerated styles take the same arguments and
should produce the same results, except for round-off and precision
issues.

These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
USER-OMP and OPT packages, respectively.  They are only enabled if
LAMMPS was built with those packages.  See the "Making
LAMMPS"_Section_start.html#start_3 section for more info.

You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the "-suffix command-line
switch"_Section_start.html#start_7 when you invoke LAMMPS, or you can
use the "suffix"_suffix.html command in your input script.

See "Section 5"_Section_accelerate.html of the manual for
more instructions on how to use the accelerated styles effectively.

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[Mixing, shift, table, tail correction, restart, rRESPA info]:

None of these pair styles support mixing.  Thus, coefficients for all
I,J pairs must be specified explicitly.

All of these pair styles support the "pair_modify"_pair_modify.html
shift option for the energy of the pair interaction.

The "pair_modify"_pair_modify.html table options is not relevant for
the Morse pair styles.

None of these pair styles support the "pair_modify"_pair_modify.html
tail option for adding long-range tail corrections to energy and
pressure.

All of these pair styles write their information to "binary restart
files"_restart.html, so pair_style and pair_coeff commands do not need
to be specified in an input script that reads a restart file.

These pair styles can only be used via the {pair} keyword of the
"run_style respa"_run_style.html command.  They do not support the
{inner}, {middle}, {outer} keywords.

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[Restrictions:]

The {morse/smooth/linear} pair style is only enabled if LAMMPS was
built with the USER-MISC package.  See the "Making
LAMMPS"_Section_start.html#start_3 section for more info.

The {morse/soft} pair style is only enabled if LAMMPS was built with
the USER-FEP package.  See the "Making
LAMMPS"_Section_start.html#start_3 section for more info.

[Related commands:]

"pair_coeff"_pair_coeff.html

[Default:] none
