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Re: [lammps-users] TIP4P interaction with other atoms (buckingham)
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Re: [lammps-users] TIP4P interaction with other atoms (buckingham)

From: Axel Kohlmeyer <akohlmey@...24...>
Date: Tue, 21 Nov 2017 17:41:14 -0500

On Tue, Nov 21, 2017 at 4:39 PM, jamal kazazi <jamalkazazi@...36.....1420...> wrote:
Dear all,
I need to define buckingham interaction between the oxygen in TIP4P and an atom type 3. 
I define:
kspace_style pppm/tip4p 1e-5
pair_style hybrid buck/coul/long 8.5 lj/cut/tip4p/long 1 2 1 1 01546 8.5
pair_coeff  1 3  buck/coul/long       2.78e4   0.297         #TIP4P oxygen and type 3
pair_coeff  1 1  lj/cut/tip4p/long    0.18521  3.1589       #TIP4P oxygen - TIP4P oxygen
My question is: does specifying buck/coul/long take care of the shifted charge center for oxygen completely (both short and long range)?
But if that's the case, then using lj/cut/coul/long instead of lj/cut/tip4p/long for 1-1 interaction should make no difference.
it seems like it's okey to do this.

​that depends on what your model is. with your setup, 1 3 interactions using the buck/coul/long ​potential, will "see" only the oxygen and hydrogen atoms and the charge on the M point will not be seen, but rather assumed to be on the location of the oxygen atoms, since this is a coul/long potential and not a tip4p/long potential.

if you don't want this, you have to describe your TIP4P model as explicit 4-site potential, time integrate it with fix rigid (since you cannot apply SHAKE to that geometry) and then replace all tip4p variants (pair and kspace) with the the regular ones.


Thank you in advance

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Dr. Axel Kohlmeyer  akohlmey@...12...24...
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.