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@ -24,11 +24,9 @@
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<I>mesh/disp</I> value = x y z
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x,y,z = grid size in each dimension for 1/r^6 dispersion
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<I>order</I> value = N
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N = gridextent of Gaussian for PPPM or MSM mapping of charge to grid
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N = extent of Gaussian for PPPM or MSM mapping of charge to grid
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<I>order/disp</I> value = N
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N = extent of Gaussian for PPPM mapping of dispersion term to grid
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<I>order/split</I> value = N
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N = order of Taylor series used to split the potential between different MSM levels
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<I>force</I> value = accuracy (force units)
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<I>gewald</I> value = rinv (1/distance units)
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rinv = G-ewald parameter for Coulombics
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@ -45,7 +43,7 @@
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>kspace_modify mesh 24 24 30 order 6 order/split 3
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<PRE>kspace_modify mesh 24 24 30 order 6
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kspace_modify slab 3.0
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</PRE>
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<P><B>Description:</B>
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@ -88,14 +86,6 @@ dispersion term extends when it is mapped to the grid in kspace style
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<I>pppm/disp</I>. It has the same meaning as the <I>order</I> setting for
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Coulombics.
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</P>
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<P>The <I>order/split</I> keyword determines the order of the Taylor series
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used to split the potential between different MSM grid levels, and can
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range from 2 and 6. <A HREF = "#Hardy">(Hardy)</A> recommends that the <I>order/split</I>
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be roughly half of the order parameter. For example, the default MSM
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order is 4 and the default split order is 2. For higher accuracy in
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MSM, one can use order 10 and <I>order/split</I> 5 or 6, though this will
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increase the interpolation cost as described above.
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</P>
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<P>The PPPM order parameter may be reset by LAMMPS when it sets up the
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FFT grid if the implied grid stencil extends beyond the grid cells
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owned by neighboring processors. Typically this will only occur when
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@ -179,9 +169,8 @@ option. Support for those <I>pppm</I> variants will be added later.
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<P><B>Default:</B>
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</P>
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<P>The option defaults are mesh = mesh/disp = 0 0 0, order = order/disp =
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5 (PPPM), order = 4 (MSM), order/split = 2 (MSM), force = -1.0, gewald
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= gewald/disp = 0.0, slab = 1.0, compute = yes, and diff = ik (PPPM),
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diff = ad (MSM).
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5 (PPPM), order = 4 (MSM), force = -1.0, gewald = gewald/disp = 0.0,
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slab = 1.0, compute = yes, and diff = ik (PPPM), diff = ad (MSM).
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</P>
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<HR>
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@ -189,10 +178,4 @@ diff = ad (MSM).
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<P><B>(Yeh)</B> Yeh and Berkowitz, J Chem Phys, 111, 3155 (1999).
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</P>
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<A NAME = "Hardy"></A>
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<P><B>(Hardy)</B> David, Multilevel Summation for the Fast Evaluation of
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Forces for the Simulation of Biomolecules, University of Illinois
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at Urbana-Champaign, (2006).
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</P>
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</HTML>
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@ -19,11 +19,9 @@ keyword = {mesh} or {order} or {gewald} or {slab} or (nozforce} or {compute} or
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{mesh/disp} value = x y z
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x,y,z = grid size in each dimension for 1/r^6 dispersion
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{order} value = N
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N = gridextent of Gaussian for PPPM or MSM mapping of charge to grid
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N = extent of Gaussian for PPPM or MSM mapping of charge to grid
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{order/disp} value = N
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N = extent of Gaussian for PPPM mapping of dispersion term to grid
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{order/split} value = N
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N = order of Taylor series used to split the potential between different MSM levels
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{force} value = accuracy (force units)
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{gewald} value = rinv (1/distance units)
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rinv = G-ewald parameter for Coulombics
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@ -39,7 +37,7 @@ keyword = {mesh} or {order} or {gewald} or {slab} or (nozforce} or {compute} or
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[Examples:]
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kspace_modify mesh 24 24 30 order 6 order/split 3
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kspace_modify mesh 24 24 30 order 6
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kspace_modify slab 3.0 :pre
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[Description:]
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@ -60,7 +58,7 @@ user-specified accuracy and pairwise cutoff. Values for x,y,z of
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The {mesh/disp} keyword sets the grid size for kspace style
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{pppm/disp}. This is the FFT mesh for long-range dispersion and ach
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dimension must be factorizable into powers of 2, 3, and 5. When this
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option is not set, the PPPM solver chooses its own grid size,
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option is not set, the PPPM solver chooses its own grid size,
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consistent with the user-specified accuracy and pairwise cutoff.
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Values for x,y,z of 0,0,0 unset the option.
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@ -82,14 +80,6 @@ dispersion term extends when it is mapped to the grid in kspace style
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{pppm/disp}. It has the same meaning as the {order} setting for
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Coulombics.
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The {order/split} keyword determines the order of the Taylor series
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used to split the potential between different MSM grid levels, and can
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range from 2 and 6. "(Hardy)"_#Hardy recommends that the {order/split}
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be roughly half of the order parameter. For example, the default MSM
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order is 4 and the default split order is 2. For higher accuracy in
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MSM, one can use order 10 and {order/split} 5 or 6, though this will
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increase the interpolation cost as described above.
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The PPPM order parameter may be reset by LAMMPS when it sets up the
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FFT grid if the implied grid stencil extends beyond the grid cells
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owned by neighboring processors. Typically this will only occur when
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@ -173,16 +163,10 @@ option. Support for those {pppm} variants will be added later.
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[Default:]
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The option defaults are mesh = mesh/disp = 0 0 0, order = order/disp =
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5 (PPPM), order = 4 (MSM), order/split = 2 (MSM), force = -1.0, gewald
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= gewald/disp = 0.0, slab = 1.0, compute = yes, and diff = ik (PPPM),
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diff = ad (MSM).
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5 (PPPM), order = 4 (MSM), force = -1.0, gewald = gewald/disp = 0.0,
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slab = 1.0, compute = yes, and diff = ik (PPPM), diff = ad (MSM).
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:line
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:link(Yeh)
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[(Yeh)] Yeh and Berkowitz, J Chem Phys, 111, 3155 (1999).
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:link(Hardy)
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[(Hardy)] David, Multilevel Summation for the Fast Evaluation of
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Forces for the Simulation of Biomolecules, University of Illinois
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at Urbana-Champaign, (2006).
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@ -77,7 +77,7 @@ style</A> to perform consistent short-range pairwise
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calculations. This means that the name of the pair style contains a
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matching keyword to the name of the KSpace style, as in this table:
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</P>
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<DIV ALIGN=center><TABLE BORDER=1 >
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<DIV ALIGN=center><TABLE WIDTH="0%" BORDER=1 >
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<TR ALIGN="center"><TD >Pair style </TD><TD > KSpace style </TD></TR>
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<TR ALIGN="center"><TD >coul/long </TD><TD > ewald or pppm</TD></TR>
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<TR ALIGN="center"><TD >coul/msm </TD><TD > msm</TD></TR>
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@ -161,15 +161,10 @@ as N. It may therefore be faster than the other K-space solvers for
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relatively large problems when running on large core counts.
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</P>
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<P>MSM is most competitive versus Ewald and PPPM when only relatively
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low accuracy forces, about 1% relative error or higher, are needed.
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Note that MSM speed will be poor for large MSM meshes
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(i.e. 64 x 64 x 64 or larger). Also note that use of a larger
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coulomb cutoff (i.e. 15 angstroms instead of 10 angstroms) provides
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better MSM accuracy for both the real space and grid computed forces.
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Beware that the error estimation method for MSM is not very accurate,
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so you should probably set your own mesh size and ensure that you are
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getting adequate force accuracy by doing an energy conservation test
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or comparison versus the Ewald method.
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low accuracy forces, about 1e-4 relative error or less accurate,
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are needed. Note that use of a larger coulomb cutoff (i.e. 15
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angstroms instead of 10 angstroms) provides better MSM accuracy for
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both the real space and grid computed forces.
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</P>
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<HR>
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@ -184,7 +179,7 @@ smaller than the reference force.
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</P>
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<P>The accuracy setting is used in conjunction with the pairwise cutoff
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to determine the number of K-space vectors for style <I>ewald</I> or the
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FFT grid size for style <I>pppm</I> or <I>msm</I>.
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grid size for style <I>pppm</I> or <I>msm</I>.
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</P>
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<P>RMS force errors in real space for <I>ewald</I> and <I>pppm</I> are estimated
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using equation 18 of <A HREF = "#Kolafa">(Kolafa)</A>, which is also referenced as
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@ -154,15 +154,10 @@ as N. It may therefore be faster than the other K-space solvers for
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relatively large problems when running on large core counts.
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MSM is most competitive versus Ewald and PPPM when only relatively
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low accuracy forces, about 1% relative error or higher, are needed.
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Note that MSM speed will be poor for large MSM meshes
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(i.e. 64 x 64 x 64 or larger). Also note that use of a larger
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coulomb cutoff (i.e. 15 angstroms instead of 10 angstroms) provides
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better MSM accuracy for both the real space and grid computed forces.
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Beware that the error estimation method for MSM is not very accurate,
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so you should probably set your own mesh size and ensure that you are
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getting adequate force accuracy by doing an energy conservation test
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or comparison versus the Ewald method.
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low accuracy forces, about 1e-4 relative error or less accurate,
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are needed. Note that use of a larger coulomb cutoff (i.e. 15
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angstroms instead of 10 angstroms) provides better MSM accuracy for
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both the real space and grid computed forces.
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:line
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@ -177,7 +172,7 @@ smaller than the reference force.
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The accuracy setting is used in conjunction with the pairwise cutoff
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to determine the number of K-space vectors for style {ewald} or the
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FFT grid size for style {pppm} or {msm}.
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grid size for style {pppm} or {msm}.
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RMS force errors in real space for {ewald} and {pppm} are estimated
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using equation 18 of "(Kolafa)"_#Kolafa, which is also referenced as
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