Merge pull request #669 from urpedersen/master

fix rhok - biasing long-range order

doc/src/Eqs/fix_rhok.tex

@@ -0,0 +1,11 @@
+\documentclass[12pt]{article}
+
+\begin{document}
+
+\begin{eqnarray*}
+ U &=&  \frac{1}{2} K (|\rho_{\vec{k}}| - a)^2 \\
+ \rho_{\vec{k}} &=& \sum_j^N \exp(-i\vec{k} \cdot \vec{r}_j )/\sqrt{N} \\
+ \vec{k} &=& (2\pi n_x /L_x , 2\pi n_y  /L_y , 2\pi n_z/L_z ) 
+\end{eqnarray*}
+
+\end{document}

doc/src/Section_commands.txt

@@ -728,6 +728,7 @@ package"_Section_start.html#start_3.
 "qtb"_fix_qtb.html,
 "reax/c/bonds"_fix_reax_bonds.html,
 "reax/c/species"_fix_reaxc_species.html,
+"rhok"_fix_rhok.html,
 "rx"_fix_rx.html,
 "saed/vtk"_fix_saed_vtk.html,
 "shardlow"_fix_shardlow.html,

doc/src/fix_rhok.txt

@@ -0,0 +1,57 @@
+"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
+
+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 1 all npt temp 0.8 0.8 4.0 z 2.2 2.2 8.0
+# output                             U_bias rho_k_RE  rho_k_IM  |rho_k|
+thermo_style custom step temp pzz lz f_bias f_bias\[1\] f_bias\[2\] f_bias\[3\] :pre
+
+[Description:]
+
+The fix applies an force to atoms given by the potential
+
+:c,image(Eqs/fix_rhok.jpg)
+
+as described in "(Pedersen)"_#Pedersen. 
+
+This field, that bias configurations with long-range order, 
+can be used to study crystal-liquid interfaces
+and determine melting temperatures "(Pedersen)"_#Pedersen.
+
+An example of using the interface pinning method 
+is located in the folder 
+{examples/USER/pinning} of the source code to LAMMPS.
+
+[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
+
+:line
+
+:link(Pedersen)
+[(Pedersen)] Pedersen, J. Chem. Phys., 139, 104102 (2013).
+

doc/src/fixes.txt

@@ -125,6 +125,7 @@ Fixes :h1
    fix_reaxc_species
    fix_recenter
    fix_restrain
+   fix_rhok
    fix_rigid
    fix_rx
    fix_saed_vtk

doc/src/lammps.book

@@ -254,6 +254,7 @@ fix_reaxc_species.html
 fix_recenter.html
 fix_restrain.html
 fix_rigid.html
+fix_rhok.html
 fix_rx.html
 fix_saed_vtk.html
 fix_setforce.html