"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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fix rhok command :h3

fix ID group-ID rhok nx ny nz k a :pre

ID, group-ID are documented in "fix"_fix.html command
nx, ny, nz = k-vektor of collective density field
K = spring constant of bias potential
a = anchor point of bias potential :ul

[Examples:]

fix bias all rhok 16 0 0 4.0 16.0
fix bias Bs rhok 12 12 0 10.0 24.0 :pre

[Description:]

The fix applies an force to atoms given by the potential

:c,image(Eqs/fix_rhok.jpg)

as described in "(Pedersen)"_#Pedersen. 
The energy and the value of the
collective density field can be written by including

# output                                U_bias rho_k_RE  rho_k_IM |rho_k| 
thermo_style custom step temp pzz pe lz f_bias f_bias\[1\] f_bias\[2\] f_bias\[3\] :pre

to the input script.

This field that bias long-range order 
can be used to study crystal-liquid interfaces,
and determine melting temperatures "(Pedersen)"_#Pedersen.
The folder {examples/pinning} of the source code 
contains an example of using the interface pinning method 
on the Lennard-Jones system.

[Restrictions:]

This fix is part of the MISC package.  It is only enabled if LAMMPS
was built with that package.  See the "Making
LAMMPS"_Section_start.html#start_3 section for more info.

[Related commands:]

"thermo_style"_thermo_style.html

[Default:] none

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:link(Pedersen)
[(Pedersen)] Pedersen, J. Chem. Phys., 139, 104102 (2013).