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), 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
diff --git a/doc/kspace_modify.txt b/doc/kspace_modify.txt index 19c91d3a42..47c17e04e9 100644 --- a/doc/kspace_modify.txt +++ b/doc/kspace_modify.txt @@ -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