lijiext
/
lammps
mirror of https://github.com/lammps/lammps.git
1
0
Fork 1
Code Issues Packages Projects Releases Wiki Activity

git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@8532 f3b2605a-c512-4ea7-a41b-209d697bcdaa

This commit is contained in:
sjplimp 2012-08-06 21:19:58 +00:00
parent 93181e05b0
commit e4d3494ab2
2 changed files with 28 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
doc/kspace_modify.html
View File

@ -120,10 +120,20 @@ This keyword gives you that option.
PPPM method to compute forces on particles given electrostatic
potentials on the PPPM mesh. The <I>ik</I> approach is the default. It
performs differentiation in Kspace, but uses 3 FFTs to transfer the
computed fields back to real space. The analytic differentiation, or
<I>ad</I> approach uses only 1 FFT to transfer the computed fields back to
real space, but requires a somewhat larger PPPM mesh to achieve the
same accuracy as the <I>ik</I> approach.
computed fields back to real space (total of 4 FFTs per timestep). The
analytic differentiation, or <I>ad</I> approach uses only 1 FFT to transfer
the computed fields back to real space (total of 2 FFTs per timestep),
but requires a somewhat larger PPPM mesh to achieve the same accuracy
as the <I>ik</I> approach.
</P>
<P>IMPORTANT NOTE: Currently, only the <I>pppm</I> style supports the <I>ad</I>
option. Support from other <I>pppm</I> variants will be added later.
</P>
<P>IMPORTANT NOTE: If you run the <I>ad</I> option with a constant pressure
simulation (e.g. with <A HREF = "fix_nh.html">fix npt</A>), you may see a net
slow-down. This is because the <I>ad</I> option requires more expensive
pre-computation whenever the box size changes. This happens every
step for constant-pressure simulations.
</P>
<P><B>Restrictions:</B> none
</P>

18
doc/kspace_modify.txt
View File

@ -114,10 +114,20 @@ The {diff} keyword specifies the differentiation scheme used by the
PPPM method to compute forces on particles given electrostatic
potentials on the PPPM mesh. The {ik} approach is the default. It
performs differentiation in Kspace, but uses 3 FFTs to transfer the
computed fields back to real space. The analytic differentiation, or
{ad} approach uses only 1 FFT to transfer the computed fields back to
real space, but requires a somewhat larger PPPM mesh to achieve the
same accuracy as the {ik} approach.
computed fields back to real space (total of 4 FFTs per timestep). The
analytic differentiation, or {ad} approach uses only 1 FFT to transfer
the computed fields back to real space (total of 2 FFTs per timestep),
but requires a somewhat larger PPPM mesh to achieve the same accuracy
as the {ik} approach.
IMPORTANT NOTE: Currently, only the {pppm} style supports the {ad}
option. Support from other {pppm} variants will be added later.
IMPORTANT NOTE: If you run the {ad} option with a constant pressure
simulation (e.g. with "fix npt"_fix_nh.html), you may see a net
slow-down. This is because the {ad} option requires more expensive
pre-computation whenever the box size changes. This happens every
step for constant-pressure simulations.
[Restrictions:] none