Dear Paul,

Many thanks for your email. I am using March-2-2012 version and below is the input script:

I have set the ewald accuracy to 1e-6 but when I go to the ewald.cpp, ewald::compute function and print the accuracy I get the value of 0.00033.

I wonder if you could elaborate on this problem

Thanks

Arshia

# (1) Initialization

units real

dimension 3

boundary p p p

newton on

atom_style full

#processors 2 2 2

kspace_style ewald 1.0e-6

pair_style lj/cut/coul/long 11.2664

pair_modify table 0

bond_style harmonic

angle_style harmonic

# dihedral_style harmonic

# improper_style cvff

# (2) Atom definition

read_data Prop_atom_True.lammps05

# (3) Settings

neighbor 2.0 bin

special_bonds lj/coul 0.0 0.0 1.0

# (5) Dynamics

timestep 1.0

velocity all create 300 4928459 rot yes dist uniform

fix 1 all nvt temp 300.0 300.0 100.0

thermo_style custom step etotal ke temp pe ebond eangle edihed eimp evdwl ecoul elong press pxx pyy pzz

thermo 500

restart 500000 Pre_poly.restart

dump 1 all atom 10000 arc_1st.class2

dump_modify 1 image yes scale yes flush yes

dump 2 all dcd 10000 traj_1st.dcd

run 500000

undump 1

undump 2

unfix 1

Youâ€™re probably looking at the absolute RMS force accuracy. The 1e-6 value you input specifies the estimated relative force accuracy. The difference is that the latter includes a normalization factor. Both the absolute and relative accuracies are printed to the screen and the logfile during Ewald initialization. You should see something like this:

estimated absolute RMS force accuracy = 0.000332064

estimated relative force accuracy = 1e-06

Please review the documentation for more information:

http://lammps.sandia.gov/doc/kspace_modify.html

http://lammps.sandia.gov/doc/kspace_style.html

Especially:

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*.

RMS force errors in real space for *ewald* and *pppm* are estimated using equation 18 of (Kolafa), which is also referenced as equation 9 of (Petersen). RMS force errors in K-space for *ewald* are estimated using equation 11 of (Petersen), which is similar to equation 32 of (Kolafa). RMS force errors in K-space for *pppm* are estimated using equation 38 of (Deserno).

Paul