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@ -170,7 +170,7 @@
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<li>one or more keyword/value pairs may be appended</li>
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</ul>
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<pre class="literal-block">
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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>xy</em> or <em>yz</em> or <em>xz</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>scalexy</em> or <em>scaleyz</em> or <em>scalexz</em> or <em>flip</em> or <em>fixedpoint</em>
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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>xy</em> or <em>yz</em> or <em>xz</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>scalexy</em> or <em>scaleyz</em> or <em>scalexz</em> or <em>flip</em> or <em>fixedpoint</em> or <em>update</em>
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<em>temp</em> values = Tstart Tstop Tdamp
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Tstart,Tstop = external temperature at start/end of run
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Tdamp = temperature damping parameter (time units)
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@ -201,6 +201,7 @@ keyword = <em>temp</em> or <em>iso</em> or <em>aniso</em> or <em>tri</em> or <em
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<em>flip</em> value = <em>yes</em> or <em>no</em> = allow or disallow box flips when it becomes highly skewed
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<em>fixedpoint</em> values = x y z
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x,y,z = perform barostat dilation/contraction around this point (distance units)
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<em>update</em> value = <em>dipole</em> update dipole orientation (only for sphere variants)
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</pre>
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</div>
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<div class="section" id="examples">
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@ -235,12 +236,12 @@ correctly, the time-averaged temperature and stress tensor of the
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particles will match the target values specified by Tstart/Tstop and
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Pstart/Pstop.</p>
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<p>The equations of motion used are those of Shinoda et al in
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<a class="reference internal" href="pair_sdk.html#shinoda"><span>(Shinoda)</span></a>, which combine the hydrostatic equations of
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Martyna, Tobias and Klein in <a class="reference internal" href="fix_rigid.html#martyna"><span>(Martyna)</span></a> with the strain
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<a class="reference internal" href="#shinoda"><span>(Shinoda)</span></a>, which combine the hydrostatic equations of
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Martyna, Tobias and Klein in <a class="reference internal" href="#martyna"><span>(Martyna)</span></a> with the strain
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energy proposed by Parrinello and Rahman in
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<a class="reference internal" href="fix_nh_eff.html#parrinello"><span>(Parrinello)</span></a>. The time integration schemes closely
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<a class="reference internal" href="#parrinello"><span>(Parrinello)</span></a>. The time integration schemes closely
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follow the time-reversible measure-preserving Verlet and rRESPA
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integrators derived by Tuckerman et al in <a class="reference internal" href="run_style.html#tuckerman"><span>(Tuckerman)</span></a>.</p>
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integrators derived by Tuckerman et al in <a class="reference internal" href="#tuckerman"><span>(Tuckerman)</span></a>.</p>
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<hr class="docutils" />
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<p>The thermostat parameters for fix styles <em>nvt</em> and <em>npt</em> is specified
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using the <em>temp</em> keyword. Other thermostat-related keywords are
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@ -397,7 +398,7 @@ freedom. A value of 0 corresponds to no thermostatting of the
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barostat variables.</p>
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<p>The <em>mtk</em> keyword controls whether or not the correction terms due to
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Martyna, Tuckerman, and Klein are included in the equations of motion
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<a class="reference internal" href="fix_rigid.html#martyna"><span>(Martyna)</span></a>. Specifying <em>no</em> reproduces the original
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<a class="reference internal" href="#martyna"><span>(Martyna)</span></a>. Specifying <em>no</em> reproduces the original
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Hoover barostat, whose volume probability distribution function
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differs from the true NPT and NPH ensembles by a factor of 1/V. Hence
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using <em>yes</em> is more correct, but in many cases the difference is
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@ -406,7 +407,7 @@ negligible.</p>
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scheme at little extra cost. The initial and final updates of the
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thermostat variables are broken up into <em>tloop</em> substeps, each of
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length <em>dt</em>/<em>tloop</em>. This corresponds to using a first-order
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Suzuki-Yoshida scheme <a class="reference internal" href="run_style.html#tuckerman"><span>(Tuckerman)</span></a>. The keyword <em>ploop</em>
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Suzuki-Yoshida scheme <a class="reference internal" href="#tuckerman"><span>(Tuckerman)</span></a>. The keyword <em>ploop</em>
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does the same thing for the barostat thermostat.</p>
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<p>The keyword <em>nreset</em> controls how often the reference dimensions used
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to define the strain energy are reset. If this keyword is not used,
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@ -447,6 +448,11 @@ to <em>fixedpoint</em>, then the lower periodic boundaries will remain at
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far. In all cases, the particle trajectories are unaffected by the
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chosen value, except for a time-dependent constant translation of
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positions.</p>
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<p>If the <em>update</em> keyword is used with the <em>dipole</em> value, then the
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orientation of the dipole moment of each particle is also updated
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during the time integration. This option should be used for models
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where a dipole moment is assigned to finite-size particles,
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e.g. spheroids via use of the <a class="reference internal" href="atom_style.html"><em>atom_style hybrid sphere dipole</em></a> command.</p>
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<hr class="docutils" />
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<div class="admonition note">
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<p class="first admonition-title">Note</p>
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@ -560,6 +566,18 @@ to undergo a slow random walk. This can be mitigated by resetting
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the momentum at infrequent intervals using the
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<a class="reference internal" href="fix_momentum.html"><em>fix momentum</em></a> command.</p>
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</div>
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<div class="admonition note">
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<p class="first admonition-title">Note</p>
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<p class="last">This implementation has been shown to conserve linear momentum
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up to machine precision under NVT dynamics. Under NPT dynamics,
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for a system with zero initial total linear momentum, the total
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momentum fluctuates close to zero. It may occasionally undergo brief
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excursions to non-negligible values, before returning close to zero.
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Over long simulations, this has the effect of causing the center-of-mass
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to undergo a slow random walk. This can be mitigated by resetting
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the momentum at infrequent intervals using the
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<a class="reference internal" href="fix_momentum.html"><em>fix momentum</em></a> command.</p>
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</div>
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<hr class="docutils" />
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<p>The fix npt and fix nph commands can be used with rigid bodies or
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mixtures of rigid bodies and non-rigid particles (e.g. solvent). But
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@ -26,7 +26,7 @@ fix ID group-ID style_name keyword value ... :pre
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ID, group-ID are documented in "fix"_fix.html command :ulb,l
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style_name = {nvt} or {npt} or {nph} :l
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one or more keyword/value pairs may be appended :l
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keyword = {temp} or {iso} or {aniso} or {tri} or {x} or {y} or {z} or {xy} or {yz} or {xz} or {couple} or {tchain} or {pchain} or {mtk} or {tloop} or {ploop} or {nreset} or {drag} or {dilate} or {scalexy} or {scaleyz} or {scalexz} or {flip} or {fixedpoint}
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keyword = {temp} or {iso} or {aniso} or {tri} or {x} or {y} or {z} or {xy} or {yz} or {xz} or {couple} or {tchain} or {pchain} or {mtk} or {tloop} or {ploop} or {nreset} or {drag} or {dilate} or {scalexy} or {scaleyz} or {scalexz} or {flip} or {fixedpoint} or {update}
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{temp} values = Tstart Tstop Tdamp
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Tstart,Tstop = external temperature at start/end of run
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Tdamp = temperature damping parameter (time units)
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{scalexz} value = {yes} or {no} = scale xz with lz
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{flip} value = {yes} or {no} = allow or disallow box flips when it becomes highly skewed
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{fixedpoint} values = x y z
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x,y,z = perform barostat dilation/contraction around this point (distance units) :pre
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x,y,z = perform barostat dilation/contraction around this point (distance units)
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{update} value = {dipole} update dipole orientation (only for sphere variants) :pre
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:ule
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[Examples:]
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@ -327,6 +328,13 @@ far. In all cases, the particle trajectories are unaffected by the
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chosen value, except for a time-dependent constant translation of
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positions.
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If the {update} keyword is used with the {dipole} value, then the
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orientation of the dipole moment of each particle is also updated
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during the time integration. This option should be used for models
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where a dipole moment is assigned to finite-size particles,
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e.g. spheroids via use of the "atom_style hybrid sphere
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dipole"_atom_style.html command.
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:line
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NOTE: Using a barostat coupled to tilt dimensions {xy}, {xz}, {yz} can
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@ -450,6 +458,16 @@ to undergo a slow random walk. This can be mitigated by resetting
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the momentum at infrequent intervals using the
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"fix momentum"_fix_momentum.html command.
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NOTE: This implementation has been shown to conserve linear momentum
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up to machine precision under NVT dynamics. Under NPT dynamics,
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for a system with zero initial total linear momentum, the total
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momentum fluctuates close to zero. It may occasionally undergo brief
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excursions to non-negligible values, before returning close to zero.
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Over long simulations, this has the effect of causing the center-of-mass
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to undergo a slow random walk. This can be mitigated by resetting
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the momentum at infrequent intervals using the
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"fix momentum"_fix_momentum.html command.
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:line
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The fix npt and fix nph commands can be used with rigid bodies or
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@ -163,8 +163,8 @@ assumes point particles and only updates their position and velocity.</p>
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<p>If the <em>update</em> keyword is used with the <em>dipole</em> value, then the
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orientation of the dipole moment of each particle is also updated
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during the time integration. This option should be used for models
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where a dipole moment is assigned to particles via use of the
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<a class="reference internal" href="atom_style.html"><em>atom_style dipole</em></a> command.</p>
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where a dipole moment is assigned to finite-size particles,
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e.g. spheroids via use of the <a class="reference internal" href="atom_style.html"><em>atom_style hybrid sphere dipole</em></a> command.</p>
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<hr class="docutils" />
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<p>Styles with a <em>cuda</em>, <em>gpu</em>, <em>intel</em>, <em>kk</em>, <em>omp</em>, or <em>opt</em> suffix are
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functionally the same as the corresponding style without the suffix.
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@ -39,8 +39,9 @@ assumes point particles and only updates their position and velocity.
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If the {update} keyword is used with the {dipole} value, then the
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orientation of the dipole moment of each particle is also updated
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during the time integration. This option should be used for models
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where a dipole moment is assigned to particles via use of the
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"atom_style dipole"_atom_style.html command.
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where a dipole moment is assigned to finite-size particles,
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e.g. spheroids via use of the "atom_style hybrid sphere
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dipole"_atom_style.html command.
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:line
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