diff --git a/doc/kspace_modify.html b/doc/kspace_modify.html index 2c5b55fdcd..44ff5d8648 100644 --- a/doc/kspace_modify.html +++ b/doc/kspace_modify.html @@ -23,8 +23,9 @@ x,y,z = PPPM FFT grid size in each dimension order value = N N = grid extent of Gaussian for PPPM mapping of each charge - gewald value = r - r = PPPM G-ewald parameter + force value = accuracy (force units) + gewald value = rinv (1/distance units) + rinv = PPPM G-ewald parameter slab value = volfactor volfactor = ratio of the total extended volume used in the 2d approximation compared with the volume of the simulation domain @@ -66,15 +67,25 @@ 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 force keyword overrides the relative accuracy parameter set by +the kspace_style command with an absolute +accuracy. The accuracy determines the RMS error in per-atom forces +calculated by the long-range solver and is thus specified in force +units. A negative value for the accuracy setting means to use the +relative accuracy parameter. The accuracy setting is 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. +

The gewald keyword sets the value of the Ewald or PPPM G-ewald -parameter. Without this setting, LAMMPS chooses the parameter -automatically as a function of cutoff, precision, grid spacing, etc. -This means it can vary from one simulation to the next which may not -be desirable for matching a KSpace solver to a pre-tabulated pairwise -potential. This setting can also be useful if Ewald or PPPM fails to -choose a good grid spacing and G-ewald parameter automatically. If -the value is set to 0.0, LAMMPS will choose the G-ewald parameter -automatically. +parameter as rinv in reciprocal distance units. Without this +setting, LAMMPS chooses the parameter automatically as a function of +cutoff, precision, grid spacing, etc. This means it can vary from one +simulation to the next which may not be desirable for matching a +KSpace solver to a pre-tabulated pairwise potential. This setting can +also be useful if Ewald or PPPM fails to choose a good grid spacing +and G-ewald parameter automatically. If the value is set to 0.0, +LAMMPS will choose the G-ewald parameter automatically.

The slab keyword allows an Ewald or PPPM solver to be used for a systems that are periodic in x,y but non-periodic in z - a @@ -98,8 +109,8 @@ option is explained in the paper by (Yeh).

Default:

-

The option defaults are mesh = 0 0 0, order = 5, gewald = 0.0, and -slab = 1.0. +

The option defaults are mesh = 0 0 0, order = 5, force = -1.0, gewald += 0.0, and slab = 1.0.

diff --git a/doc/kspace_modify.txt b/doc/kspace_modify.txt index 282d9ff7a0..6a4b54d93c 100644 --- a/doc/kspace_modify.txt +++ b/doc/kspace_modify.txt @@ -18,8 +18,9 @@ keyword = {mesh} or {order} or {gewald} or {slab} :l x,y,z = PPPM FFT grid size in each dimension {order} value = N N = grid extent of Gaussian for PPPM mapping of each charge - {gewald} value = r - r = PPPM G-ewald parameter + {force} value = accuracy (force units) + {gewald} value = rinv (1/distance units) + rinv = PPPM G-ewald parameter {slab} value = volfactor volfactor = ratio of the total extended volume used in the 2d approximation compared with the volume of the simulation domain :pre @@ -60,15 +61,25 @@ 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 {force} keyword overrides the relative accuracy parameter set by +the "kspace_style"_kspace_style.html command with an absolute +accuracy. The accuracy determines the RMS error in per-atom forces +calculated by the long-range solver and is thus specified in force +units. A negative value for the accuracy setting means to use the +relative accuracy parameter. The accuracy setting is 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}. + The {gewald} keyword sets the value of the Ewald or PPPM G-ewald -parameter. Without this setting, LAMMPS chooses the parameter -automatically as a function of cutoff, precision, grid spacing, etc. -This means it can vary from one simulation to the next which may not -be desirable for matching a KSpace solver to a pre-tabulated pairwise -potential. This setting can also be useful if Ewald or PPPM fails to -choose a good grid spacing and G-ewald parameter automatically. If -the value is set to 0.0, LAMMPS will choose the G-ewald parameter -automatically. +parameter as {rinv} in reciprocal distance units. Without this +setting, LAMMPS chooses the parameter automatically as a function of +cutoff, precision, grid spacing, etc. This means it can vary from one +simulation to the next which may not be desirable for matching a +KSpace solver to a pre-tabulated pairwise potential. This setting can +also be useful if Ewald or PPPM fails to choose a good grid spacing +and G-ewald parameter automatically. If the value is set to 0.0, +LAMMPS will choose the G-ewald parameter automatically. The {slab} keyword allows an Ewald or PPPM solver to be used for a systems that are periodic in x,y but non-periodic in z - a @@ -92,8 +103,8 @@ option is explained in the paper by "(Yeh)"_#Yeh. [Default:] -The option defaults are mesh = 0 0 0, order = 5, gewald = 0.0, and -slab = 1.0. +The option defaults are mesh = 0 0 0, order = 5, force = -1.0, gewald += 0.0, and slab = 1.0. :line diff --git a/doc/kspace_style.html b/doc/kspace_style.html index 5d6c200f5d..cab5f9843e 100644 --- a/doc/kspace_style.html +++ b/doc/kspace_style.html @@ -18,25 +18,25 @@ @@ -119,13 +119,23 @@ dispersion forces in a Lennard-Jones or Buckingham potential, see the pair_style lj/coul or pair_style buck/coul commands.

-

A precision value of 1.0e-4 means one part in 10000. This setting is -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. +

The specified accuracy determines the relative RMS error in per-atom +forces calculated by the long-range solver. It is set as a +dimensionless number, relative to the force that two unit point +charges (e.g. 2 monovalent ions) exert on each other at a distance of +1 Angstrom. This reference value was chosen as representative of the +magnitude of electrostatic forces in atomic systems. Thus an accuracy +value of 1.0e-4 means that the RMS error will be a factor of 10000 +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 +FFT grid size for style pppm.

See the kspace_modify command for additional -options of the K-space solvers that can be set. +options of the K-space solvers that can be set, including a force +option for setting an absoulte RMS error in forces, as opposed to a +relative RMS error.

diff --git a/doc/kspace_style.txt b/doc/kspace_style.txt index d13dbf68d9..e0d1079631 100644 --- a/doc/kspace_style.txt +++ b/doc/kspace_style.txt @@ -14,25 +14,25 @@ kspace_style style value :pre style = {none} or {ewald} or {pppm} or {pppm/cg} or {pppm/tip4p} or {ewald/n} or {pppm/gpu} or {ewald/omp} or {pppm/omp} or {pppm/proxy} :ulb,l {none} value = none - {ewald} value = precision - precision = desired accuracy - {pppm} value = precision - precision = desired accuracy - {pppm/cg} value = precision (smallq) - precision = desired accuracy + {ewald} value = accuracy + accuracy = desired relative error in forces + {pppm} value = accuracy + accuracy = desired relative error in forces + {pppm/cg} value = accuracy (smallq) + accuracy = desired relative error in forces smallq = cutoff for charges to be considered (optional) (charge units) - {pppm/tip4p} value = precision - precision = desired accuracy - {ewald/n} value = precision - precision = desired accuracy - {pppm/gpu} value = precision - precision = desired accuracy - {ewald/omp} value = precision - precision = desired accuracy - {pppm/omp} value = precision - precision = desired accuracy - {pppm/proxy} value = precision - precision = desired accuracy :pre + {pppm/tip4p} value = accuracy + accuracy = desired relative error in forces + {ewald/n} value = accuracy + accuracy = desired relative error in forces + {pppm/gpu} value = accuracy + accuracy = desired relative error in forces + {ewald/omp} value = accuracy + accuracy = desired relative error in forces + {pppm/omp} value = accuracy + accuracy = desired relative error in forces + {pppm/proxy} value = accuracy + accuracy = desired relative error in forces :pre :ule [Examples:] @@ -114,13 +114,23 @@ dispersion forces in a Lennard-Jones or Buckingham potential, see the "pair_style lj/coul"_pair_lj_coul.html or "pair_style buck/coul"_pair_buck_coul.html commands. -A precision value of 1.0e-4 means one part in 10000. This setting is -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}. +The specified {accuracy} determines the relative RMS error in per-atom +forces calculated by the long-range solver. It is set as a +dimensionless number, relative to the force that two unit point +charges (e.g. 2 monovalent ions) exert on each other at a distance of +1 Angstrom. This reference value was chosen as representative of the +magnitude of electrostatic forces in atomic systems. Thus an accuracy +value of 1.0e-4 means that the RMS error will be a factor of 10000 +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 +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. +options of the K-space solvers that can be set, including a {force} +option for setting an absoulte RMS error in forces, as opposed to a +relative RMS error. :line