forked from lijiext/lammps
git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@15140 f3b2605a-c512-4ea7-a41b-209d697bcdaa
This commit is contained in:
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@ -55,8 +55,11 @@ Restrictions
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""""""""""""
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The compute *dpd* is only available if LAMMPS is built with the
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USER-DPD package and requires the :doc:`atom_style dpd <atom_style>`.
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This command is part of the USER-DPD package. It is only enabled if
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LAMMPS was built with that package. See the :ref:`Making LAMMPS <start_3>` section for more info.
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This command also requires use of the :doc:`atom_style dpd <atom_style>`
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command.
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Related commands
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""""""""""""""""
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@ -46,8 +46,11 @@ Restrictions
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""""""""""""
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The compute *dpd/atom* is only available if LAMMPS is built with the
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USER-DPD package.
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This command is part of the USER-DPD package. It is only enabled if
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LAMMPS was built with that package. See the :ref:`Making LAMMPS <start_3>` section for more info.
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This command also requires use of the :doc:`atom_style dpd <atom_style>`
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command.
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Related commands
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""""""""""""""""
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@ -186,6 +186,7 @@ of :ref:`this page <cmd_5>`.
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* :doc:`drag <fix_drag>` - drag atoms towards a defined coordinate
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* :doc:`dt/reset <fix_dt_reset>` - reset the timestep based on velocity, forces
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* :doc:`efield <fix_efield>` - impose electric field on system
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* :doc:`ehex <fix_ehex>` - ehanced heat exchange algorithm
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* :doc:`enforce2d <fix_enforce2d>` - zero out z-dimension velocity and force
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* :doc:`evaporate <fix_evaporate>` - remove atoms from simulation periodically
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* :doc:`external <fix_external>` - callback to an external driver program
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@ -71,69 +71,33 @@ hundred (LJ and SPC/E water) with little computational overhead.
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In both algorithms (non-translational) kinetic energy is constantly
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swapped between regions (reservoirs) to impose a heat flux onto the
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system. The equations of motion are therefore modified if a particle
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*i* is located inside a reservoir
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.. image:: Eqs/fix_ehex01.jpg
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:align: center
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where
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.. image:: Eqs/fix_ehex02.jpg
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:align: center
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We use
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.. image:: Eqs/fix_ehex03.jpg
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:align: center
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to label those parts of the simulation box which are not
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thermostatted.) The input parameter *region-ID* of this fix
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corresponds to *k*\ . The energy swap is modelled by introducing an
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:math:`i` is located inside a reservoir :math:`\Gamma_\ *k*\` where :math:`k>0`. We
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use :math:`\Gamma_\ *0*\` to label those parts of the simulation box which
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are not thermostatted.) The input parameter *region-ID* of this fix
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corresponds to :math:`k`. The energy swap is modelled by introducing an
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additional thermostatting force to the equations of motion, such that
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the time evolution of coordinates and momenta of particle *i* becomes
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:ref:`(Wirnsberger) <Wirnsberger>`
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the time evolution of coordinates and momenta of particle :math:`i`
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becomes :ref:`(Wirnsberger) <Wirnsberger>`
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.. image:: Eqs/fix_ehex04.jpg
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.. image:: src/Eqs/fix_ehex_eom.jpg
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:align: center
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The thermostatting force is given by
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.. image:: Eqs/fix_ehex05.jpg
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.. image:: src/Eqs/fix_ehex_f.jpg
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:align: center
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where
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.. image:: Eqs/fix_ehex06.jpg
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:align: center
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is the mass and
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.. image:: Eqs/fix_ehex07.jpg
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:align: center
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maps the particle position to the respective reservoir. The quantity
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.. image:: Eqs/fix_ehex08.jpg
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:align: center
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corresponds to the input parameter *F*\ , which is the energy flux into
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the reservoir. Furthermore,
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.. image:: Eqs/fix_ehex09.jpg
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:align: center
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and
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.. image:: Eqs/fix_ehex10.jpg
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:align: center
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denote the non-translational kinetic
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energy and the centre of mass velocity of that reservoir. The
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thermostatting force does not affect the centre of mass velocities of
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the individual reservoirs and the entire simulation box. A derivation
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of the equations and details on the numerical implementation with
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velocity Verlet in LAMMPS can be found in reference
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"(Wirnsberger)"#_Wirnsberger.
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where :math:`m_i` is the mass and :math:`k(\mathbf r_i)` maps the particle
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position to the respective reservoir. The quantity
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:math:`F_*\Gamma_*k(\mathbf r_i)**` corresponds to the input parameter
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*F*\ , which is the energy flux into the reservoir. Furthermore,
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:math:`K_*\Gamma_*k(\mathbf r_i)**` and :math:`v_*\Gamma_*k(\mathbf r_i)**`
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denote the non-translational kinetic energy and the centre of mass
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velocity of that reservoir. The thermostatting force does not affect
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the centre of mass velocities of the individual reservoirs and the
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entire simulation box. A derivation of the equations and details on
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the numerical implementation with velocity Verlet in LAMMPS can be
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found in reference "(Wirnsberger)"#_Wirnsberger.
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.. note::
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@ -193,7 +157,7 @@ constraints will be satisfied.
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bond distances, which goes to zero with order three in the
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timestep. For example, in a simulation of SPC/E water with a timestep
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of 2 fs the maximum relative error in the bond distances was found to
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be on the order of :c,image(Eqs/fix_ehex07.jpg) for relatively large
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be on the order of :math:`10^\ *-7*\` for relatively large
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temperature gradients. A higher precision can be achieved by
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decreasing the timestep.
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@ -220,8 +184,7 @@ was built with that package. See the :ref:`Making LAMMPS <start_3>` section for
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Related commands
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""""""""""""""""
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:doc:`fix heat <fix_heat>`, :doc:`fix thermal/conductivity <fix_thermal_conductivity>`,
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:doc:`compute temp <compute_temp>`, :doc:`compute temp/region <compute_temp_region>`
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:doc:`fix heat <fix_heat>`, :doc:`fix thermal/conductivity <fix_thermal_conductivity>`, :doc:`compute temp <compute_temp>`, :doc:`compute temp/region <compute_temp_region>`
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**Default:** none
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@ -164,8 +164,10 @@ output options.</p>
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</div>
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<div class="section" id="restrictions">
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<h2>Restrictions</h2>
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<p>The compute <em>dpd</em> is only available if LAMMPS is built with the
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USER-DPD package and requires the <a class="reference internal" href="atom_style.html"><span class="doc">atom_style dpd</span></a>.</p>
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<p>This command is part of the USER-DPD package. It is only enabled if
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LAMMPS was built with that package. See the <a class="reference internal" href="Section_start.html#start-3"><span class="std std-ref">Making LAMMPS</span></a> section for more info.</p>
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<p>This command also requires use of the <a class="reference internal" href="atom_style.html"><span class="doc">atom_style dpd</span></a>
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command.</p>
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</div>
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<div class="section" id="related-commands">
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<h2>Related commands</h2>
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@ -162,8 +162,10 @@ and temperature (dpdTheta) <a class="reference internal" href="units.html"><span
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</div>
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<div class="section" id="restrictions">
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<h2>Restrictions</h2>
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<p>The compute <em>dpd/atom</em> is only available if LAMMPS is built with the
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USER-DPD package.</p>
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<p>This command is part of the USER-DPD package. It is only enabled if
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LAMMPS was built with that package. See the <a class="reference internal" href="Section_start.html#start-3"><span class="std std-ref">Making LAMMPS</span></a> section for more info.</p>
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<p>This command also requires use of the <a class="reference internal" href="atom_style.html"><span class="doc">atom_style dpd</span></a>
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command.</p>
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</div>
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<div class="section" id="related-commands">
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<h2>Related commands</h2>
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@ -292,6 +292,7 @@ of <a class="reference internal" href="Section_commands.html#cmd-5"><span class=
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<li><a class="reference internal" href="fix_drag.html"><span class="doc">drag</span></a> - drag atoms towards a defined coordinate</li>
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<li><a class="reference internal" href="fix_dt_reset.html"><span class="doc">dt/reset</span></a> - reset the timestep based on velocity, forces</li>
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<li><a class="reference internal" href="fix_efield.html"><span class="doc">efield</span></a> - impose electric field on system</li>
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<li><a class="reference internal" href="fix_ehex.html"><span class="doc">ehex</span></a> - ehanced heat exchange algorithm</li>
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<li><a class="reference internal" href="fix_enforce2d.html"><span class="doc">enforce2d</span></a> - zero out z-dimension velocity and force</li>
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<li><a class="reference internal" href="fix_evaporate.html"><span class="doc">evaporate</span></a> - remove atoms from simulation periodically</li>
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<li><a class="reference internal" href="fix_external.html"><span class="doc">external</span></a> - callback to an external driver program</li>
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@ -187,39 +187,27 @@ hundred (LJ and SPC/E water) with little computational overhead.</p>
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<p>In both algorithms (non-translational) kinetic energy is constantly
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swapped between regions (reservoirs) to impose a heat flux onto the
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system. The equations of motion are therefore modified if a particle
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<em>i</em> is located inside a reservoir</p>
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<img alt="Eqs/fix_ehex01.jpg" class="align-center" src="Eqs/fix_ehex01.jpg" />
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<p>where</p>
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<img alt="Eqs/fix_ehex02.jpg" class="align-center" src="Eqs/fix_ehex02.jpg" />
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<p>We use</p>
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<img alt="Eqs/fix_ehex03.jpg" class="align-center" src="Eqs/fix_ehex03.jpg" />
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<p>to label those parts of the simulation box which are not
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thermostatted.) The input parameter <em>region-ID</em> of this fix
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corresponds to <em>k</em>. The energy swap is modelled by introducing an
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<span class="math">\(i\)</span> is located inside a reservoir <span class="math">\(\Gamma_\ *k*\` where :math:`k>0\)</span>. We
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use <span class="math">\(\Gamma_\ *0*\` to label those parts of the simulation box which
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are not thermostatted.) The input parameter *region-ID* of this fix
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corresponds to :math:`k\)</span>. The energy swap is modelled by introducing an
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additional thermostatting force to the equations of motion, such that
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the time evolution of coordinates and momenta of particle <em>i</em> becomes
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<a class="reference internal" href="#wirnsberger"><span class="std std-ref">(Wirnsberger)</span></a></p>
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<img alt="Eqs/fix_ehex04.jpg" class="align-center" src="Eqs/fix_ehex04.jpg" />
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the time evolution of coordinates and momenta of particle <span class="math">\(i\)</span>
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becomes <a class="reference internal" href="#wirnsberger"><span class="std std-ref">(Wirnsberger)</span></a></p>
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<img alt="src/Eqs/fix_ehex_eom.jpg" class="align-center" src="src/Eqs/fix_ehex_eom.jpg" />
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<p>The thermostatting force is given by</p>
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<img alt="Eqs/fix_ehex05.jpg" class="align-center" src="Eqs/fix_ehex05.jpg" />
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<p>where</p>
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<img alt="Eqs/fix_ehex06.jpg" class="align-center" src="Eqs/fix_ehex06.jpg" />
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<p>is the mass and</p>
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<img alt="Eqs/fix_ehex07.jpg" class="align-center" src="Eqs/fix_ehex07.jpg" />
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<p>maps the particle position to the respective reservoir. The quantity</p>
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<img alt="Eqs/fix_ehex08.jpg" class="align-center" src="Eqs/fix_ehex08.jpg" />
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<p>corresponds to the input parameter <em>F</em>, which is the energy flux into
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the reservoir. Furthermore,</p>
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<img alt="Eqs/fix_ehex09.jpg" class="align-center" src="Eqs/fix_ehex09.jpg" />
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<p>and</p>
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<img alt="Eqs/fix_ehex10.jpg" class="align-center" src="Eqs/fix_ehex10.jpg" />
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<p>denote the non-translational kinetic
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energy and the centre of mass velocity of that reservoir. The
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thermostatting force does not affect the centre of mass velocities of
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the individual reservoirs and the entire simulation box. A derivation
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of the equations and details on the numerical implementation with
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velocity Verlet in LAMMPS can be found in reference
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“(Wirnsberger)”#_Wirnsberger.</p>
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<img alt="src/Eqs/fix_ehex_f.jpg" class="align-center" src="src/Eqs/fix_ehex_f.jpg" />
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<p>where <span class="math">\(m_i\)</span> is the mass and <span class="math">\(k(\mathbf r_i)\)</span> maps the particle
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position to the respective reservoir. The quantity
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<span class="math">\(F_*\Gamma_*k(\mathbf r_i)**\)</span> corresponds to the input parameter
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<em>F</em>, which is the energy flux into the reservoir. Furthermore,
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<span class="math">\(K_*\Gamma_*k(\mathbf r_i)**\)</span> and <span class="math">\(v_*\Gamma_*k(\mathbf r_i)**\)</span>
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denote the non-translational kinetic energy and the centre of mass
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velocity of that reservoir. The thermostatting force does not affect
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the centre of mass velocities of the individual reservoirs and the
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entire simulation box. A derivation of the equations and details on
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the numerical implementation with velocity Verlet in LAMMPS can be
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found in reference “(Wirnsberger)”#_Wirnsberger.</p>
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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 fix only integrates the thermostatting force and must be
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@ -270,7 +258,7 @@ implementation of the eHEX algorithm introduces a small error in the
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bond distances, which goes to zero with order three in the
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timestep. For example, in a simulation of SPC/E water with a timestep
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of 2 fs the maximum relative error in the bond distances was found to
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be on the order of :c,image(Eqs/fix_ehex07.jpg) for relatively large
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be on the order of :math:<a href="#id1"><span class="problematic" id="id2">`</span></a>10^<em>-7</em>` for relatively large
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temperature gradients. A higher precision can be achieved by
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decreasing the timestep.</p>
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</div>
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@ -290,8 +278,7 @@ was built with that package. See the <a class="reference internal" href="Sectio
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</div>
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<div class="section" id="related-commands">
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<h2>Related commands</h2>
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<p><a class="reference internal" href="fix_heat.html"><span class="doc">fix heat</span></a>, <a class="reference internal" href="fix_thermal_conductivity.html"><span class="doc">fix thermal/conductivity</span></a>,
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<a class="reference internal" href="compute_temp.html"><span class="doc">compute temp</span></a>, <a class="reference internal" href="compute_temp_region.html"><span class="doc">compute temp/region</span></a></p>
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<p><a class="reference internal" href="fix_heat.html"><span class="doc">fix heat</span></a>, <a class="reference internal" href="fix_thermal_conductivity.html"><span class="doc">fix thermal/conductivity</span></a>, <a class="reference internal" href="compute_temp.html"><span class="doc">compute temp</span></a>, <a class="reference internal" href="compute_temp_region.html"><span class="doc">compute temp/region</span></a></p>
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<p><strong>Default:</strong> none</p>
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<hr class="docutils" />
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<p id="ikeshoji"><strong>(Ikeshoji)</strong> Ikeshoji and Hafskjold, Molecular Physics, 81, 251-261 (1994).</p>
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