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Commit 84e9e3b6 authored by ext-calvo_p's avatar ext-calvo_p
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Resolve "Wrong equation name"

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......@@ -284,65 +284,71 @@ More details will be given in Version 2.0.0.
[[sec.fieldsolvers.p3m]]
=== Particle-Particle-Particle-Mesh (latexmath:[P^3M]) Solver
The latexmath:[P^3M] solver of Hockney and Eastwood <<bib.hockneyandeastwood>>
The latexmath:[P^3M] solver of Hockney and Eastwood <<bib.hockneyandeastwood>>
takes into account collisions between particles in an electrostatic
one-one PIC simulation (every simulation particle is a
real particle) in an efficient manner compared to PIC with excessive mesh refinement or
a direct N-body summation. The main idea behind this approach is a splitting of the
one-one PIC simulation (every simulation particle is a real particle) in an
efficient manner compared to PIC with excessive mesh refinement or a direct
N-body summation. The main idea behind this approach is a splitting of the
total force latexmath:[F] into two components
[latexmath#eq-oneterm]
[latexmath#eq-p3mForce]
++++
F = F_{sr} + F_{lr}
++++
where latexmath:[F_{sr}] is the short-range component which can be
computed efficiently in the real-space with a small cut-off radius by direct summation,
whereas latexmath:[F_{lr}] is the long-range component and this can be calculated efficiently
in the Fourier space with a few Fourier modes due to its rapid spectral decay. Consequently,
we split the Green's function latexmath:[G] also into two components as
where latexmath:[F_{sr}] is the short-range component which can be computed
efficiently in the real-space with a small cut-off radius by direct summation,
whereas latexmath:[F_{lr}] is the long-range component and this can be
calculated efficiently in the Fourier space with a few Fourier modes due to its
rapid spectral decay. Consequently, we split the Green's function
latexmath:[G] also into two components as
[latexmath#eq-oneterm]
[latexmath#eq-p3mGreen]
++++
G(r) = \psi(r) + \phi(r) = \frac{1 - f(r)}{r} + \frac{f(r)}{r}
++++
where latexmath:[\psi(r)] is the short-range or the particle-particle Green's function and
latexmath:[\phi(r)] is the long range or the particle-mesh Green's function. Apart from certain
smoothness conditions there is a lot of flexibility in the choice of latexmath:[f(r)] and this
leads to different screening shapes for the particles. The standard choice from the Ewald
summation corresponds to <<bib.p3mulmerthesis>>, <<bib.p3mhuenenberger>>
where latexmath:[\psi(r)] is the short-range or the particle-particle
Green's function and latexmath:[\phi(r)] is the long range or the
particle-mesh Green's function. Apart from certain smoothness conditions
there is a lot of flexibility in the choice of latexmath:[f(r)] and this
leads to different screening shapes for the particles. The standard choice
from the Ewald summation corresponds to <<bib.p3mulmerthesis>>, <<bib.p3mhuenenberger>>
[latexmath#eq-oneterm]
[latexmath#eq-p3mEwald]
++++
f(r) = erf(\alpha r)
++++
where latexmath:[\alpha] is the interaction splitting parameter which determines the relative
significance of the particle-particle part to the particle-mesh part. It is usually chosen as
latexmath:[\alpha = C/r_c], where latexmath:[r_c] is the cut-off or interaction radius and latexmath:[C] is
a postive constant. This choice of Green's function corresponds to Gaussian shaped screening
charges. In OPAL, the `P3M` solver uses this Green's function when the option is
specifed as `STANDARD`.
where latexmath:[\alpha] is the interaction splitting parameter which
determines the relative significance of the particle-particle part to the
particle-mesh part. It is usually chosen as latexmath:[\alpha = C/r_c], where
latexmath:[r_c] is the cut-off or interaction radius and latexmath:[C] is
a postive constant. This choice of Green's function corresponds to Gaussian
shaped screening charges. In OPAL, the `P3M` solver uses this Green's function
when the option is specifed as `STANDARD`.
Another popular choice for latexmath:[f(r)] corresponds to truncated polynomials of different orders
as given in Table I of appendix B in <<bib.p3mhuenenberger>>. The lowest order function in the table corresponds to
Another popular choice for latexmath:[f(r)] corresponds to truncated polynomials
of different orders as given in Table I of appendix B in <<bib.p3mhuenenberger>>.
The lowest order function in the table corresponds to
[latexmath#eq-oneterm]
[latexmath#eq-p3mLowFunc]
++++
f(r) = \frac{\xi(3 - \xi^2)}{2}
++++
where latexmath:[\xi = r/r_c]. We use the integrated version of this Green's function when we specify the option
for Green's function as `INTEGRATED` in the `P3M` solver in OPAL. The reason to use this one instead of the integrated
version of the standard Green's function described before is the availability of a closed form expression when performing
the integration.
where latexmath:[\xi = r/r_c]. We use the integrated version of this Green's
function when we specify the option for Green's function as `INTEGRATED` in the
`P3M` solver in OPAL. The reason to use this one instead of the integrated
version of the standard Green's function described before is the availability
of a closed form expression when performing the integration.
[[sec.fieldsolvers.P3M.use]]
==== Use of latexmath:[P^3M] solver
At the moment, the `P3M` solver is only available in _OPAL-T_ when emission is not active. It uses `OPEN`
boundary conditions. The interaction splitting parameter latexmath:[\alpha] is used only for the `STANDARD`
Green's function option. We can specify the solver in the input file as follows
At the moment, the `P3M` solver is only available in _OPAL-T_ when emission
is not active. It uses `OPEN` boundary conditions. The interaction splitting
parameter latexmath:[\alpha] is used only for the `STANDARD` Green's function
option. We can specify the solver in the input file as follows
[source]
----
......
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