"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)

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pair_style ufm command :h3
pair_style ufm/gpu command :h3
pair_style ufm/omp command :h3
pair_style ufm/opt command :h3

[Syntax:]

pair_style ufm cutoff :pre

cutoff = global cutoff for {ufm} interactions (distance units) :ul

[Examples:]

pair_style ufm 4.0
pair_coeff 1 1 100.0 1.0 2.5
pair_coeff * * 100.0 1.0 :pre


pair_style ufm 4.0
pair_coeff * * 10.0 1.0
variable prefactor equal ramp(10,100)
fix 1 all adapt 1 pair ufm epsilon * * v_prefactor :pre

[Description:]

Style {ufm} computes pairwise interactions using the Uhlenbeck-Ford model (UFM) potential "(Paula Leite2016)"_#PL2 which is given by

:c,image(Eqs/pair_ufm.jpg)

where rc is the cutoff, sigma is a distance-scale and epsilon is an energy-scale, i.e., a product of Boltzmann constant kB, temperature T and the Uhlenbeck-Ford p-parameter which is responsible
to control the softness of the interactions "(Paula Leite2017)"_#PL1.
This model is useful as a reference system for fluid-phase free-energy calculations "(Paula Leite2016)"_#PL2.

The following coefficients must be defined for each pair of atom 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, or by mixing as described below:

epsilon (energy units)
sigma (distance units)
cutoff (distance units) :ul

The last coefficient is optional.  If not specified, the global {ufm}
cutoff is used.


The "fix adapt"_fix_adapt.html command can be used to vary epsilon and sigma for this pair style over the course of a simulation, in which case
pair_coeff settings for epsilon and sigma must still be specified, but will be
overridden.  For example these commands will vary the prefactor epsilon for
all pairwise interactions from 10.0 at the beginning to 100.0 at the end
of a run:

variable prefactor equal ramp(10,100)
fix 1 all adapt 1 pair ufm epsilon * * v_prefactor :pre

NOTE: The thermodynamic integration procedure can be performed with this potential using "fix adapt"_fix_adapt.html. This command will rescale the force on each atom by varying a scale variable, which always starts with value 1.0. The syntax is the same described above, however, changing epsilon to scale. A detailed explanation of how to use this command and perform nonequilibrium thermodynamic integration in LAMMPS is given in the paper by "(Freitas)"_#Freitas2.

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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 on the "Speed packages"_Speed_packages.html doc
page.  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 "Build
package"_Build_package.html doc page 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"_Run_options.html when you invoke LAMMPS, or you can use the
"suffix"_suffix.html command in your input script.

See the "Speed packages"_Speed_packages.html doc page for more
instructions on how to use the accelerated styles effectively.

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

For atom type pairs I,J and I != J, the A coefficient and cutoff
distance for this pair style can be mixed.  A is always mixed via a
{geometric} rule.  The cutoff is mixed according to the pair_modify
mix value.  The default mix value is {geometric}.  See the
"pair_modify" command for details.

This pair style support the "pair_modify"_pair_modify.html shift option for the energy of the pair interaction.

The "pair_modify"_pair_modify.html table and tail are not relevant for this
pair style.

This pair style does not support the "pair_modify"_pair_modify.html tail option for adding long-range tail corrections to energy and pressure.

This pair style writes its 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.

This pair style can only be used via the {pair} keyword of the
"run_style respa"_run_style.html command.  It does not support the
{inner}, {middle}, {outer} keywords.

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[Restrictions:] none

[Related commands:]

"pair_coeff"_pair_coeff.html, "fix adapt"_fix_adapt.html

[Default:] none


:link(PL1)
[(Paula Leite2017)] Paula Leite, Santos-Florez, and de Koning, Phys Rev E, 96,
32115 (2017).

:link(PL2)
[(Paula Leite2016)] Paula Leite , Freitas, Azevedo, and de Koning, J Chem Phys, 126,
044509 (2016).

:link(Freitas2)
[(Freitas)] Freitas, Asta, and de Koning, Computational Materials Science, 112, 333 (2016).
