<li>ID, group-ID are documented in <aclass="reference internal"href="fix.html"><spanclass="doc">fix</span></a> command</li>
</ul>
<preclass="literal-block">
one or more keyword value pairs may be appended
keyword = <em>temp</em> or <em>iso</em> or <em>aniso</em> or <em>tri</em> or <em>x</em> or <em>y</em> or <em>z</em> or <em>couple</em> or <em>tchain</em> or <em>pchain</em> or <em>mtk</em> or <em>tloop</em> or <em>ploop</em> or <em>nreset</em> or <em>drag</em> or <em>dilate</em> or <em>scaleyz</em> or <em>scalexz</em> or <em>scalexy</em>
<em>temp</em> values = Value1 Value2 Tdamp
Value1, Value2 = Nose-Hoover target temperatures, ignored by Hugoniostat
Tdamp = temperature damping parameter (time units)
<em>iso</em> or <em>aniso</em> or <em>tri</em> values = Pstart Pstop Pdamp
Pstart,Pstop = scalar external pressures, must be equal (pressure units)
Pdamp = pressure damping parameter (time units)
<em>x</em> or <em>y</em> or <em>z</em> or <em>xy</em> or <em>yz</em> or <em>xz</em> values = Pstart Pstop Pdamp
Pstart,Pstop = external stress tensor components, must be equal (pressure units)
Pdamp = stress damping parameter (time units)
<em>couple</em> = <em>none</em> or <em>xyz</em> or <em>xy</em> or <em>yz</em> or <em>xz</em>
<em>tchain</em> value = length of thermostat chain (1 = single thermostat)
<em>pchain</em> values = length of thermostat chain on barostat (0 = no thermostat)
<em>mtk</em> value = <em>yes</em> or <em>no</em> = add in MTK adjustment term or not
<em>tloop</em> value = number of sub-cycles to perform on thermostat
<em>ploop</em> value = number of sub-cycles to perform on barostat thermostat
<em>nreset</em> value = reset reference cell every this many timesteps
<em>drag</em> value = drag factor added to barostat/thermostat (0.0 = no drag)
<em>dilate</em> value = <em>all</em> or <em>partial</em>
<em>scaleyz</em> value = <em>yes</em> or <em>no</em> = scale yz with lz
<em>scalexz</em> value = <em>yes</em> or <em>no</em> = scale xz with lz
<em>scalexy</em> value = <em>yes</em> or <em>no</em> = scale xy with ly
It performs time integration of the Hugoniostat equations
of motion developed by Ravelo et al. <aclass="reference internal"href="pair_lj_cubic.html#ravelo"><spanclass="std std-ref">(Ravelo)</span></a>.
These equations compress the system to a state with average
axial stress or pressure equal to the specified target value
and that satisfies the Rankine-Hugoniot (RH)
jump conditions for steady shocks.</p>
<p>The compression can be performed
either
hydrostatically (using keyword <em>iso</em>, <em>aniso</em>, or <em>tri</em>) or uniaxially
(using keywords <em>x</em>, <em>y</em>, or <em>z</em>). In the hydrostatic case,
the cell dimensions change dynamically so that the average axial stress
in all three directions converges towards the specified target value.
In the uniaxial case, the chosen cell dimension changes dynamically
so that the average
axial stress in that direction converges towards the target value. The
other two cell dimensions are kept fixed (zero lateral strain).</p>
<p>This leads to the following additional restrictions on the keywords:</p>
<ulclass="simple">
<li>One and only one of the following keywords should be used: <em>iso</em>, <em>aniso</em>, <em>tri</em>, <em>x</em>, <em>y</em>, <em>z</em></li>
<li>The specified initial and final target pressures must be the same.</li>
<li>The keywords <em>xy</em>, <em>xz</em>, <em>yz</em> may not be used.</li>
<li>The only admissible value for the couple keyword is <em>xyz</em>, which has the same effect as keyword <em>iso</em></li>
<li>The <em>temp</em> keyword must be used to specify the time constant for kinetic energy relaxation, but initial and final target temperature values are ignored.</li>
</ul>
<p>Essentially, a Hugoniostat simulation is an NPT simulation in which the
user-specified target temperature is replaced with a time-dependent
target temperature Tt obtained from the following equation:</p>
should not use any other time integration fix, such as <aclass="reference internal"href="fix_nve.html"><spanclass="doc">fix nve</span></a> on atoms to which this fix is applied. Likewise,
this fix should not be used on atoms that have their temperature
controlled by another fix - e.g. by <aclass="reference internal"href="fix_nh.html"><spanclass="doc">fix langevin</span></a> or <aclass="reference internal"href="fix_temp_rescale.html"><spanclass="doc">fix temp/rescale</span></a> commands.</p>
</div>
<hrclass="docutils"/>
<p>This fix computes a temperature and pressure at each timestep. To do
this, the fix creates its own computes of style “temp” and “pressure”,
as if one of these two sets of commands had been issued:</p>
<p>See the <aclass="reference internal"href="compute_temp.html"><spanclass="doc">compute temp</span></a> and <aclass="reference internal"href="compute_pressure.html"><spanclass="doc">compute pressure</span></a> commands for details. Note that the
IDs of the new computes are the fix-ID + underscore + “temp” or fix_ID
+ underscore + “press”. The group for
the new computes is “all” since pressure is computed for the entire
system.</p>
<p>Note that these are NOT the computes used by thermodynamic output (see
the <aclass="reference internal"href="thermo_style.html"><spanclass="doc">thermo_style</span></a> command) with ID = <em>thermo_temp</em>
and <em>thermo_press</em>. This means you can change the attributes of this
fix’s temperature or pressure via the
<aclass="reference internal"href="compute_modify.html"><spanclass="doc">compute_modify</span></a> command or print this temperature
or pressure during thermodynamic output via the <aclass="reference internal"href="thermo_style.html"><spanclass="doc">thermo_style custom</span></a> command using the appropriate compute-ID.
It also means that changing attributes of <em>thermo_temp</em> or
<em>thermo_press</em> will have no effect on this fix.</p>
<p>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 <aclass="reference internal"href="Section_start.html#start-3"><spanclass="std std-ref">Making LAMMPS</span></a> section for more info.</p>
<p>You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the <aclass="reference internal"href="Section_start.html#start-7"><spanclass="std std-ref">-suffix command-line switch</span></a> when you invoke LAMMPS, or you can
use the <aclass="reference internal"href="suffix.html"><spanclass="doc">suffix</span></a> command in your input script.</p>
<p>See <aclass="reference internal"href="Section_accelerate.html"><spanclass="doc">Section_accelerate</span></a> of the manual for
more instructions on how to use the accelerated styles effectively.</p>
included in the definition of internal energy E when calculating the value
of Delta in the above equation.</p>
<p>These fixes compute a global scalar and a global vector of quantities,
which can be accessed by various <aclass="reference internal"href="Section_howto.html#howto-15"><spanclass="std std-ref">output commands</span></a>. The scalar value calculated by
these fixes is “extensive”; the vector values are “intensive”.</p>
<p>The scalar is the cumulative energy change due to the fix.</p>
<p>The vector stores three quantities unique to this fix (Delta, Us, and up),
followed by all the internal Nose/Hoover thermostat and barostat
variables defined for <aclass="reference internal"href="fix_nh.html"><spanclass="doc">fix npt</span></a>. Delta is the deviation
of the temperature from the target temperature, given by the above equation.
Us and up are the shock and particle velocity corresponding to a steady
shock calculated from the RH conditions. They have units of distance/time.</p>
</div>
<divclass="section"id="restrictions">
<h2>Restrictions</h2>
<p>This fix style is part of the SHOCK package. It is only enabled if
LAMMPS was built with that package. See the <aclass="reference internal"href="Section_start.html#start-3"><spanclass="std std-ref">Making LAMMPS</span></a> section for more info.</p>
<p>All the usual restrictions for <aclass="reference internal"href="fix_nh.html"><spanclass="doc">fix npt</span></a> apply,
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