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@ -31,10 +31,14 @@ by itself to measure the heat flux between a hot and cold reservoir of
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particles or to calculate a thermal conductivity using the Green-Kubo
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formalism.
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</P>
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<P>See the <A HREF = "fix_thermal_conductivity.html">fix thermal/conductivity</A>
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command for details on how to compute thermal conductivity in an
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alternate way, via the Muller-Plathe method.
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</P>
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<P>The compute takes a <I>pe-ID</I> argument which is the ID of a <A HREF = "compute_pe_atom.html">compute
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pe/atom</A> that calculates per-atom potential
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energy. It should be defined for the same group used by compute
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heat/flux, though LAMMPS does not check for this.
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energy. Normally, it should be defined for the same group used by
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compute heat/flux, though LAMMPS does not check for this.
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</P>
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<P>The Green-Kubo formulas relate the ensemble average of the
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auto-correlation of the heat flux J to the thermal conductivity kappa.
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@ -43,28 +47,27 @@ auto-correlation of the heat flux J to the thermal conductivity kappa.
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</CENTER>
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<CENTER><IMG SRC = "Eqs/heat_flux_J.jpg">
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</CENTER>
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<P>Ei is the per-atom energy (potential and kinetic). The potential term
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is calculated by the compute <I>pe-ID</I> specified as an argument to
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the compute heat/flux command.
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<P>Ei is the per-atom energy (potential and kinetic). The potential
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portion is calculated by the compute <I>pe-ID</I> specified as an argument
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to the compute heat/flux command.
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</P>
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<P>IMPORTANT NOTE: The per-atom potential energy calculated by the
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<I>pe-ID</I> compute should only include pairwise energy, to be consistent
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with the full heat-flux calculation. Thus if any bonds, angles, etc
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exist in the system, the compute should limit its calculation to only
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the pair contribution. E.g. it could be defined as
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with the second virial-like term in the formula for J. Thus if any
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bonds, angles, etc exist in the system, the compute should limit its
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calculation to only the pair contribution. E.g. it could be defined
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as follows. Note that if <I>pair</I> is not listed as the last argument,
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it will be included by default, but so will other contributions such
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as bond, angle, etc.
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</P>
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<PRE>compute myPE all pe/atom pair
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</PRE>
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<P>Note that if <I>pair</I> is not listed as the last argument, it will be
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included by default, but so will other contributions such as bond,
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angle, etc.
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</P>
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<P>The heat flux J is calculated by this compute for pairwise
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interactions for any I,J pair where one of the 2 atoms in is the
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compute group. It can be output every so many timesteps (e.g. via the
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thermo_style custom command). Then as post-processing steps, an
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autocorrelation can be performed, its integral estimated, and the
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Green-Kubo formula evaluated.
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<P>The second term of the heat flux equation for J is calculated by
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compute heat/flux for pairwise interactions for any I,J pair where one
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of the 2 atoms in is the compute group. It can be output every so
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many timesteps (e.g. via the thermo_style custom command). Then as
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post-processing steps, an autocorrelation can be performed, its
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integral estimated, and the Green-Kubo formula evaluated.
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</P>
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<P>Here is an example of this procedure. First a LAMMPS input script for
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solid Ar is appended below. A Python script
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@ -100,7 +103,9 @@ included in this calculation.
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<P>To use this compute you must define an atom_style, such as dpd or
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granular, that communicates the velocites of ghost atoms.
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</P>
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<P><B>Related commands:</B> none
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "fix_thermal_conductivity.html">fix thermal/conductivity</A>
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</P>
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<P><B>Default:</B> none
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</P>
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@ -28,6 +28,10 @@ by itself to measure the heat flux between a hot and cold reservoir of
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particles or to calculate a thermal conductivity using the Green-Kubo
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formalism.
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See the "fix thermal/conductivity"_fix_thermal_conductivity.html
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command for details on how to compute thermal conductivity in an
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alternate way, via the Muller-Plathe method.
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The compute takes a {pe-ID} argument which is the ID of a "compute
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pe/atom"_compute_pe_atom.html that calculates per-atom potential
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energy. Normally, it should be defined for the same group used by
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@ -96,7 +100,9 @@ included in this calculation.
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To use this compute you must define an atom_style, such as dpd or
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granular, that communicates the velocites of ghost atoms.
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[Related commands:] none
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[Related commands:]
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"fix thermal/conductivity"_fix_thermal_conductivity.html
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[Default:] none
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@ -52,6 +52,10 @@ and measure the response as the resulting heat flux. In the
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Muller-Plathe method, the heat flux is imposed, and the temperature
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gradient is the system's response.
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</P>
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<P>See the <A HREF = "compute_heat_flux.html">compute heat/flux</A> command for details
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on how to compute thermal conductivity in an alternate way, via the
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Green-Kubo formalism.
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</P>
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<P>The simulation box is divided into <I>Nbin</I> layers in the <I>edim</I>
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direction, where the layer 1 is at the low end of that dimension and
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the layer <I>Nbin</I> is at the high end. Every N steps, Nswap pairs of
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@ -141,7 +145,8 @@ bewteen solvent particles.
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "fix_ave_spatial.html">fix ave/spatial</A>, <A HREF = "fix_viscosity.html">fix
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viscosity</A>
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viscosity</A>, <A HREF = "compute_heat_flux.html">compute
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heat/flux</A>
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</P>
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<P><B>Default:</B>
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</P>
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@ -42,6 +42,10 @@ and measure the response as the resulting heat flux. In the
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Muller-Plathe method, the heat flux is imposed, and the temperature
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gradient is the system's response.
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See the "compute heat/flux"_compute_heat_flux.html command for details
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on how to compute thermal conductivity in an alternate way, via the
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Green-Kubo formalism.
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The simulation box is divided into {Nbin} layers in the {edim}
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direction, where the layer 1 is at the low end of that dimension and
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the layer {Nbin} is at the high end. Every N steps, Nswap pairs of
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@ -131,7 +135,8 @@ bewteen solvent particles.
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[Related commands:]
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"fix ave/spatial"_fix_ave_spatial.html, "fix
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viscosity"_fix_viscosity.html
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viscosity"_fix_viscosity.html, "compute
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heat/flux"_compute_heat_flux.html
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[Default:]
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