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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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sjplimp 2008-08-20 22:23:13 +00:00
parent 569a6a37da
commit 1bb9bf1e62
4 changed files with 34 additions and 2 deletions
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15
doc/kspace_modify.html
View File

@ -51,7 +51,20 @@ Values for x,y,z of 0,0,0 unset the option.
<P>The <I>order</I> keyword determines how many grid spacings an atom's charge
extends when it is mapped to the FFT grid in kspace style pppm. The
default for this parameter is 5, which means each charge spans 5 grid
cells in each dimension.
cells in each dimension. The larger the value of this parameter, the
smaller the FFT grid will need to be to achieve the requested
precision. Conversely, the smaller the order value, the larger the
grid will be. Note that there is an inherent trade-off involved: a
small grid will lower the cost of FFTs, but a large order parameter
will increase the cost of intepolating charge/fields to/from the grid.
And vice versa.
</P>
<P>The order parameter may be reset by LAMMPS when it sets up the PPPM
FFT grid if the implied grid stencil extends beyond the grid cells
owned by neighboring processors. Typically this will only occur when
small problems are run on large numbers of processors. A warning will
be generated indicating the order parameter is being reduced to allow
LAMMPS to run the problem.
</P>
<P>The <I>gewald</I> keyword sets the value of the PPPM G-ewald parameter.
Without this setting, LAMMPS chooses the parameter automatically as a

15
doc/kspace_modify.txt
View File

@ -45,7 +45,20 @@ Values for x,y,z of 0,0,0 unset the option.
The {order} keyword determines how many grid spacings an atom's charge
extends when it is mapped to the FFT grid in kspace style pppm. The
default for this parameter is 5, which means each charge spans 5 grid
cells in each dimension.
cells in each dimension. The larger the value of this parameter, the
smaller the FFT grid will need to be to achieve the requested
precision. Conversely, the smaller the order value, the larger the
grid will be. Note that there is an inherent trade-off involved: a
small grid will lower the cost of FFTs, but a large order parameter
will increase the cost of intepolating charge/fields to/from the grid.
And vice versa.
The order parameter may be reset by LAMMPS when it sets up the PPPM
FFT grid if the implied grid stencil extends beyond the grid cells
owned by neighboring processors. Typically this will only occur when
small problems are run on large numbers of processors. A warning will
be generated indicating the order parameter is being reduced to allow
LAMMPS to run the problem.
The {gewald} keyword sets the value of the PPPM G-ewald parameter.
Without this setting, LAMMPS chooses the parameter automatically as a

3
doc/kspace_style.html
View File

@ -85,6 +85,9 @@ used in conjunction with the pairwise cutoff to determine the number
of K-space vectors for style <I>ewald</I> or the FFT grid size for style
<I>pppm</I>.
</P>
<P>See the <A HREF = "kspace_modify.html">kspace_modify</A> command for additional
options of the K-space solvers that can be set.
</P>
<P><B>Restrictions:</B>
</P>
<P>A simulation must be 3d and periodic in all dimensions to use an Ewald

3
doc/kspace_style.txt
View File

@ -80,6 +80,9 @@ used in conjunction with the pairwise cutoff to determine the number
of K-space vectors for style {ewald} or the FFT grid size for style
{pppm}.
See the "kspace_modify"_kspace_modify.html command for additional
options of the K-space solvers that can be set.
[Restrictions:]
A simulation must be 3d and periodic in all dimensions to use an Ewald