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Re: [ESPResSo-devel] User Guide on ELC and noneutralization
From: |
Vincent Ballenegger |
Subject: |
Re: [ESPResSo-devel] User Guide on ELC and noneutralization |
Date: |
Fri, 24 Feb 2012 11:52:59 +0100 |
User-agent: |
KMail/1.13.5 (Linux/2.6.34.7-0.5-default; KDE/4.4.4; i686; ; ) |
Hi Stefan,
> Also, there is this thing with the "-noneutralization" command when dealing
> with non-neutral systems. There is no information about that command in
> the user guide as well. I now figured out for myself, that one has to add
> that command, but I find its name somehow misleading. Actually when
> activating that feature there IS a neutralization done by the artificially
> added homogeneous background, so I would say its name should rather be
> neutralization, or even better let it get that information from the total
> charge of the system itself.
The name "-noneutralization" for this option is indeed somewhat misleading. It
originates from the fact that this option kills an unwanted effect (creation
of a parabolic potential) associated to the homogeneous neutralization
inherited from the underlying P3M method in P3M/ELC.
The way one can define energies and forces in a simulation of a slab system
carrying a net charge is explained in details in paper
V. Ballenegger, A. Arnold, J.J. Cerdà , "Simulations of non-neutral slab
systems with long-range electrostatic interactions in 2D periodic boundary
conditions", J. Chem. Phys. 131: 094107 (2009)
The option -noneutralization corresponds to use what is called the "background
charge correction" (bcc) defined by eq. (28) in that paper.
Personally, I think that this option should be activated automatically in
Espresso when simulating a charged slab with P3M/ELC. The name
"noneutralization" could be dropped entirely. When simulating a slab system
with a net charge, Espresso could output a message "Warning: system with a
non-zero net charge. Using background charge correction, see Ref. ...".
Regards,
Vincent Ballenegger