The compute keyword allows Kspace computations to be turned off, even though a kspace_style is defined. This is @@ -211,7 +213,9 @@ then performs analytic differentiation on the single quantity to generate the 3 components of the electric field at each grid point. This is sometimes referred to as "smoothed" PPPM. This approach requires a somewhat larger PPPM mesh to achieve the same accuracy as -the ik method. The ad method is always used for MSM. +the ik method. Currently, only the ik method (default) can be +used for a triclinic simulation cell with PPPM. The ad method is +always used for MSM.
IMPORTANT NOTE: Currently, not all PPPM styles support the ad option. Support for those PPPM variants will be added later. diff --git a/doc/kspace_modify.txt b/doc/kspace_modify.txt index 3aea97205a..f52df568dc 100644 --- a/doc/kspace_modify.txt +++ b/doc/kspace_modify.txt @@ -167,6 +167,8 @@ volfactor. This turns off all kspace forces in the z direction. The {nozforce} option is not supported by MSM. For MSM, any combination of periodic, non-periodic, or shrink-wrapped boundaries can be set using "boundary"_boundary.html (the slab approximation in not needed). +The {slab} keyword is not currently supported by Ewald or PPPM when +using a triclinic simulation cell. The {compute} keyword allows Kspace computations to be turned off, even though a "kspace_style"_kspace_style.html is defined. This is @@ -205,7 +207,9 @@ then performs analytic differentiation on the single quantity to generate the 3 components of the electric field at each grid point. This is sometimes referred to as "smoothed" PPPM. This approach requires a somewhat larger PPPM mesh to achieve the same accuracy as -the {ik} method. The {ad} method is always used for MSM. +the {ik} method. Currently, only the {ik} method (default) can be +used for a triclinic simulation cell with PPPM. The {ad} method is +always used for MSM. IMPORTANT NOTE: Currently, not all PPPM styles support the {ad} option. Support for those PPPM variants will be added later. diff --git a/doc/kspace_style.html b/doc/kspace_style.html index cc54cb8442..8fc8de3467 100644 --- a/doc/kspace_style.html +++ b/doc/kspace_style.html @@ -101,10 +101,6 @@ but in a more efficient manner than the ewald style. The 1/r^6 capability means that Lennard-Jones or Buckingham potentials can be used without a cutoff, i.e. they become full long-range potentials.
-The ewald/disp style can also be used with non-orthogonal (triclinic -symmetry) simulation boxes. It is currently the only long-range -solver that has this capability. -
The pppm style invokes a particle-particle particle-mesh solver @@ -194,7 +190,19 @@ smaller than the reference force.
The accuracy setting is used in conjunction with the pairwise cutoff to determine the number of K-space vectors for style ewald or the -grid size for style pppm or msm. +grid size for style pppm or msm. +
+Note that style pppm only computes the grid size at the beginning of +a simulation, so if the length or triclinic tilt of the simulation cell +increases dramatically during the course of the simulation, the accuracy +of the simulation may degrade. For example, for a triclinic system with +all three tilt factors set to the maximum limit, the PPPM grid should be +increased roughly by a factor of 1.5 in the y direction and 2.0 in the z +direction as compared to the same system using a cubic orthogonal simulation +cell. One way to ensure the accuracy requirement is being met is to run a +short simulation at the maximum expected tilt or length, note the required +grid size, and then use the kspace_modify mesh +command to manually set the PPPM grid size to this value.
RMS force errors in real space for ewald and pppm are estimated using equation 18 of (Kolafa), which is also referenced as @@ -242,6 +250,11 @@ more instructions on how to use the accelerated styles effectively.
Restrictions:
+The ewald/disp, ewald, pppm, and msm styles support +non-orthogonal (triclinic symmetry) simulation boxes. However, triclinic +simulation cells may not yet be supported by suffix versions of these +styles (such as pppm/cuda). +
All of the kspace styles are part of the KSPACE package. They are only enabled if LAMMPS was built with that package. See the Making LAMMPS section for more info. Note that diff --git a/doc/kspace_style.txt b/doc/kspace_style.txt index 5dd816b777..c4349e27cd 100644 --- a/doc/kspace_style.txt +++ b/doc/kspace_style.txt @@ -94,10 +94,6 @@ but in a more efficient manner than the {ewald} style. The 1/r^6 capability means that Lennard-Jones or Buckingham potentials can be used without a cutoff, i.e. they become full long-range potentials. -The {ewald/disp} style can also be used with non-orthogonal (triclinic -symmetry) simulation boxes. It is currently the only long-range -solver that has this capability. - :line The {pppm} style invokes a particle-particle particle-mesh solver @@ -187,7 +183,19 @@ smaller than the reference force. The accuracy setting is used in conjunction with the pairwise cutoff to determine the number of K-space vectors for style {ewald} or the -grid size for style {pppm} or {msm}. +grid size for style {pppm} or {msm}. + +Note that style {pppm} only computes the grid size at the beginning of +a simulation, so if the length or triclinic tilt of the simulation cell +increases dramatically during the course of the simulation, the accuracy +of the simulation may degrade. For example, for a triclinic system with +all three tilt factors set to the maximum limit, the PPPM grid should be +increased roughly by a factor of 1.5 in the y direction and 2.0 in the z +direction as compared to the same system using a cubic orthogonal simulation +cell. One way to ensure the accuracy requirement is being met is to run a +short simulation at the maximum expected tilt or length, note the required +grid size, and then use the "kspace_modify"_kspace_modify.html {mesh} +command to manually set the PPPM grid size to this value. RMS force errors in real space for {ewald} and {pppm} are estimated using equation 18 of "(Kolafa)"_#Kolafa, which is also referenced as @@ -235,6 +243,11 @@ more instructions on how to use the accelerated styles effectively. [Restrictions:] +The {ewald/disp}, {ewald}, {pppm}, and {msm} styles support +non-orthogonal (triclinic symmetry) simulation boxes. However, triclinic +simulation cells may not yet be supported by suffix versions of these +styles (such as {pppm/cuda}). + All of the kspace styles are part of the KSPACE package. They are only enabled if LAMMPS was built with that package. See the "Making LAMMPS"_Section_start.html#start_3 section for more info. Note that