forked from lijiext/lammps
100 lines
4.5 KiB
HTML
100 lines
4.5 KiB
HTML
<HTML>
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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
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</CENTER>
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<HR>
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<H3>fix ave/time command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>fix ID group-ID ave/time Nevery Nrepeat Nfreq compute-ID flag file
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</PRE>
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<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
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<LI>ave/time = style name of this fix command
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<LI>Nevery = calculate property every this many timesteps
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<LI>Nrepeat = # of times to repeat the Nevery calculation before averaging
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<LI>Nfreq = timestep frequency at which the average value is written to file
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<LI>compute-ID = ID of compute that performs the calculation
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<LI>flag = 0 for scalar quantity, 1 for vector quantity, 2 for both
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<LI>file = filename to write results to
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>fix 1 all ave/time 100 5 1000 myTemp 0 temp.stats
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Calculate one or more instantaneous quantities every few timesteps,
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average them over a longer timescale, and print the results to a file.
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This can be used to time-average any "compute" entity in LAMMPS which
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calculates a global quantity such as a temperature or pressure.
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Per-atom computes cannot be used with this fix.
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</P>
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<P>The <I>compute-ID</I> specifies a <A HREF = "compute.html">compute</A> which calculates
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the desired property. The compute must be a "global" compute that
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calculates one or more global properties rather than a "per-atom"
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compute. The compute can be previously defined in the input script.
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Or it can be a compute defined by <A HREF = "thermo_style.html">thermodynamic
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output</A> or other fixes such as <A HREF = "fix_nvt.html">fix
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nvt</A> or <A HREF = "fix_temp_rescale.html">fix temp/rescale</A>. Users
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can also write code for their own compute styles and <A HREF = "Section_modify.html">add them to
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LAMMPS</A>.
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</P>
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<P>In all these cases, the fix ave/time command uses the global scalar or
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vector calculated by the compute. See the <A HREF = "fix_ave_spatial.html">fix
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ave/spatial</A> command if you wish to average
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spatially, e.g. via a compute that calculates per-atom quantities.
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</P>
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<P>The <I>Nevery</I>, <I>Nrepeat</I>, and <I>Nfreq</I> arguments specify how the
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property will be time-averaged. The final averaged value(s) are
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computed every <I>Nfreq</I> timesteps. The average is over <I>Nrepeat</I>
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values, computed in the preceeding portion of the simulation every
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<I>Nevery</I> timesteps. Thus if Nevery=2, Nrepeat=6, and Nfreq=100, then
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values on timesteps 90,92,94,96,98,100 will be used to compute the
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final average written to the file on timestep 100. Similary for
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timesteps 190,192,194,196,198,200 on timestep 200, etc.
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</P>
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<P>The <I>flag</I> argument chooses whether the scalar and/or vector
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calculation of the compute is invoked. The former computes a single
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global value. The latter computes N global values, where N is defined
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by the compute, e.g. 6 pressure tensor components. In the vector
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case, each of the N values is averaged independently and N values are
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written to the file at each output.
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</P>
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<P>Since the calculation is performed by the compute which stores its own
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"group" definition, the group specified for this fix is ignored.
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</P>
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<P>If the compute calculates pressure, it will cause the force
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computations performed by LAMMPS (pair, bond, angle, etc) to calculate
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virial terms each Nevery timesteps. If this is more frequent than
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thermodynamic output, this adds extra cost to a simulation. However,
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if a constant pressure simulation is being run (<A HREF = "fix_npt.html">fix npt</A>
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or <A HREF = "fix_nph.html">fix nph</A>), LAMMPS is already calculating virial terms
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for the pressure every timestep.
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</P>
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<P><B>Restart, fix_modify, thermo output, run start/stop, minimize info:</B>
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</P>
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<P>No information about this fix is written to <A HREF = "restart.html">binary restart
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files</A>. None of the <A HREF = "fix_modify.html">fix_modify</A> options
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are relevant to this fix. No quantities calculated by this fix can be
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output by the <A HREF = "thermo_style.html">thermo_style custom</A> command. No
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parameter of this fix can be used with the <I>start/stop</I> keywords of
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the <A HREF = "run.html">run</A> command. This fix is not invoked during <A HREF = "minimize.html">energy
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minimization</A>.
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</P>
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<P><B>Restrictions:</B> none
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "compute.html">compute</A>, <A HREF = "fix_ave_spatial.html">fix ave/spatial</A>
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</P>
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<P><B>Default:</B> none
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</P>
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</HTML>
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