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git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@2086 f3b2605a-c512-4ea7-a41b-209d697bcdaa
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@ -51,7 +51,20 @@ Values for x,y,z of 0,0,0 unset the option.
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<P>The <I>order</I> keyword determines how many grid spacings an atom's charge
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extends when it is mapped to the FFT grid in kspace style pppm. The
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default for this parameter is 5, which means each charge spans 5 grid
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cells in each dimension.
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cells in each dimension. The larger the value of this parameter, the
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smaller the FFT grid will need to be to achieve the requested
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precision. Conversely, the smaller the order value, the larger the
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grid will be. Note that there is an inherent trade-off involved: a
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small grid will lower the cost of FFTs, but a large order parameter
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will increase the cost of intepolating charge/fields to/from the grid.
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And vice versa.
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</P>
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<P>The order parameter may be reset by LAMMPS when it sets up the PPPM
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FFT grid if the implied grid stencil extends beyond the grid cells
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owned by neighboring processors. Typically this will only occur when
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small problems are run on large numbers of processors. A warning will
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be generated indicating the order parameter is being reduced to allow
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LAMMPS to run the problem.
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</P>
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<P>The <I>gewald</I> keyword sets the value of the PPPM G-ewald parameter.
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Without this setting, LAMMPS chooses the parameter automatically as a
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@ -45,7 +45,20 @@ Values for x,y,z of 0,0,0 unset the option.
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The {order} keyword determines how many grid spacings an atom's charge
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extends when it is mapped to the FFT grid in kspace style pppm. The
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default for this parameter is 5, which means each charge spans 5 grid
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cells in each dimension.
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cells in each dimension. The larger the value of this parameter, the
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smaller the FFT grid will need to be to achieve the requested
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precision. Conversely, the smaller the order value, the larger the
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grid will be. Note that there is an inherent trade-off involved: a
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small grid will lower the cost of FFTs, but a large order parameter
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will increase the cost of intepolating charge/fields to/from the grid.
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And vice versa.
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The order parameter may be reset by LAMMPS when it sets up the PPPM
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FFT grid if the implied grid stencil extends beyond the grid cells
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owned by neighboring processors. Typically this will only occur when
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small problems are run on large numbers of processors. A warning will
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be generated indicating the order parameter is being reduced to allow
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LAMMPS to run the problem.
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The {gewald} keyword sets the value of the PPPM G-ewald parameter.
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Without this setting, LAMMPS chooses the parameter automatically as a
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@ -85,6 +85,9 @@ used in conjunction with the pairwise cutoff to determine the number
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of K-space vectors for style <I>ewald</I> or the FFT grid size for style
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<I>pppm</I>.
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</P>
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<P>See the <A HREF = "kspace_modify.html">kspace_modify</A> command for additional
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options of the K-space solvers that can be set.
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</P>
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<P><B>Restrictions:</B>
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</P>
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<P>A simulation must be 3d and periodic in all dimensions to use an Ewald
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@ -80,6 +80,9 @@ used in conjunction with the pairwise cutoff to determine the number
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of K-space vectors for style {ewald} or the FFT grid size for style
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{pppm}.
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See the "kspace_modify"_kspace_modify.html command for additional
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options of the K-space solvers that can be set.
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[Restrictions:]
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A simulation must be 3d and periodic in all dimensions to use an Ewald
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