PURPOSE
=======================
This program calculates electrostatic interactions in many particle systems
using different algorithms. It does not have a name.
INSTALL
========================
To build execute "make" in the source directory.
Prerequesits to build are an mpicc in the PATH, fftw3, the gnu scientific
library and GNU make.
RUN
========================
The binary is called "p3m". It is controlled via command line parameters.
They should be somewhat selfexplanatory, but there is detailed documentation
below. They are of the form <key> [<value>], their order is arbitrary.
EXAMPLE
========================
./p3m particles 1000 box 10 mesh 16 cao 7 rcut 3.0 method 7 alphamin 0.1
alphamax 2.5 alphastep 0.05 system_type 5
This generates a random system of 1000 particles of type 5 ( See system_type ) in a box of size 10^3.
It then calculates reference forces using an Ewald summation with machine precision,
and executes the method no. 7 ( see methods ) a mesh of 16^3 interpolation
order 7 and real space cutoff 3.0 for all alphas from 0.1 to 2.5 with a
spacing of 0.05.
PARAMETERS
=======================
* rcut <cutoff>
The realspace cutoff.
* alphamin <alphamin>
The minimal alphavalue to calculate.
* alphamax <alphamax>
The maximal alphavalue to calculate.
* alphastep <alphastep>
The distance between alphas.
* { positions <position_filename> [ forces <forces_filename> ] | paritcles
<particles> box <box> [system_type <system_type] [ charge <charge> ] }
Either a position file to read the system configuration from, or the
parameters to generate one.
The system_types are
0 SYSTEM_RANDOM uniformly distributed particles in the whole box.
1 SYSTEM_INNER_BOX randomly placed particles within [0.25*box,0.75*box)^3.
2 SYSTEM_MADELUNG A cubic cristall.
3 SYSTEM_SEPARATED_DIPOLE Randomly placed extended dipoles with distance 1.
4 SYSTEM_GAUSSIAN Gaussian distributed particles about the
center of the box.
5 SYSTEM_SLAB Particles within [0.25*box,0.75*box)x[0,box)x[0,box)
If charge is set, then the particles carry charge <charge> instead of unit charges.
The format of the position file is
# Teilchenzahl: <number_of_particles>
# Len: <box_length>
<x_1> <y_1> <z_1> <q_1>
...
<x_number_of_particles> <y_number_of_particles> <z_number_of_particles>
<q_number_of_particles>
If forces is given the reference forces are read from <forces_filename>,
the format is
<fx_1> <fy_1> <fz_1>
...
<fx_number_of_particles> <fy_number_of_particles> <fz_number_of_particles>
There have to be exactly as many lines in this file as there are particles
in the particle file. If forces is not set, the reference forces are
calculated.
* mesh <mesh_size>
The mesh size for the P3M methods.
* cao <cao>
The interpolation order for the various P3M methods.
* [mc <mc>]
The aliasing sum cutoff for the P3M influence function.
* [mc_est <mc_est>]
The aliasing sum cutoff for the P3M error estimate.
* method <method>
The method to use, where <method> is one of
0 P3M, ik differentiated, complex to complex, not interlaced.
1 P3M, ik differentiated, complex to complex, interlaced.
2 P3M, ad differentiated, complex to complex, not interlaced.
3 P3M, ad differentiated, complex to complex, interlaced.
4 Ewald summation.
6 P3M, ik differentiated, real to complex, not interlaced.
7 P3M, ad differentiated, real to complex, not interlaced.
For a description of the methods see
Deserno, Markus, and Christian Holm. "How to mesh up Ewald sums. I. A
theoretical and numerical comparison of various particle mesh routines." The
Journal of chemical physics 109 (1998): 7678.
and
Neelov, Alexey, and Christian Holm. "Interlaced P3M algorithm with analytical
and ik-differentiation." The Journal of chemical physics 132 (2010): 234103.
For a more detailed intruduction see the textbook of Hockney and Eastwood:
Hockney, Roger W., and James W. Eastwood. Computer simulation using particles. CRC Press, 2010.
* [ no_estimate ]
Disable calculation of the error estimate.
* [ outfile <filename> ]
Write output to <filename> instead of 'out.dat'.
* [ reference_out <filename>]
Write reference forces to file.
* [ system_out <filename> ]
Write system configuration to file.
* [ no_calculation ]
Skip the actual calculation.
* [ no_reference_force ]
Skip the reference force calculation even if no reference forces are given.