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Re: [lammps-users] Using shake with charge on O and massless site
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Re: [lammps-users] Using shake with charge on O and massless site


From: Axel Kohlmeyer <akohlmey@...24...>
Date: Wed, 23 May 2018 15:47:56 -0400



On Wed, May 23, 2018 at 1:30 PM, Jo <jojo412202@...24...> wrote:
Hello,

I would like to use the pair style lj/cut/tip4p/long.  I understand that this pair style automatically generates a massless dummy site just as in TIP4P and essentially moves the charge on the O atom to the massless dummy site for the coulombic calculation. 

I am using a model that has charge on both the O atom and the massless dummy site, and I would like to change the source code (pair_lj_cut_tip4p_long.cpp) slightly to accommodate this model.  Do you have any suggestions on how I can do so?

​that is not as simple as you might think. the /tip4p/ styles inherently assume, that there are only 3 LJ sites and 3 charged sites.

the easiest way to implement your model is to use 4 explicit sites, set the mass of the massless site to a tiny value (say 1.0e-10) and use fix rigid/small instead of shake.

axel.​

 

Thanks,

Jo

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--
Dr. Axel Kohlmeyer  akohlmey@...12...24...  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.