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Re: [lammps-users] improper_coeff
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Re: [lammps-users] improper_coeff


From: Vanessa Oklejas <voklejas@...24...>
Date: Mon, 04 Sep 2017 22:12:05 +0000

It's hard to say why your MD run terminates with that error- it could be multiple things. For one thing, pay attention to units that are used in this simulation. See http://lammps.sandia.gov/doc/units.html for details. For example, what units are used for the pressure in this simulation? I would have assumed that you are using "real" units, which means that you are trying to impose a high pressure on this system. Also, you need to make sure that your coefficients for bond/angle/dihedral/improper terms are consistent with the simulation units. 

On Sun, Sep 3, 2017 at 10:28 PM Hossein Geraili <geraili.hsn@...24...> wrote:
Dear Lammps users,


I simulated a box of 200 of ionic liquid molecules in NVT ensemble using:

pair_style   lj/cut/coul/long  11

kspace_style pppm 1.0e-4
when I use  fix         3 all press/berendsen iso 1184 1184 100.0, it produces an "out of range atoms - cannot compute pppm", but without this fix it is ok, but the pressure data is not well-fitted.
 before the above-mentioned error there is a warning " improper problem, which below this warning for all four atoms it produces nan values".
I used topotools to produce data file, and now, I found out that one type of my molecules improper is missing. Is there any easy way to add that improper_type. Is it possible that this missing improper type would be the cause of my bad results with great Error percent compare to exp. data?

Also, I used opls for dihedral because all the dihedrals and impropers in the article that I used to extract them is in opls form, but Lammps do not have opls form for improper, so I used cvff ( because first and third and fourth coeff. of improper were zero) and convert the coeffs to cvff form. Is this wrong? 

--
Hosein Geraili Daronkola
M.Sc.Graduated of physical chemistry
Physical Chemistry,
Department of Chemistry,
Sharif University of Technology.
geraili_hosein@...7111......



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