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Re: [lammps-users] Question about using r-respa integrator
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Re: [lammps-users] Question about using r-respa integrator

From: Pengyu Huang <>
Date: Fri, 13 Apr 2018 01:29:41 +1000

Thanks Axel for further suggestions.

Yes, I have researched the about the flexible CO2 model. As in this paper:, the harmonic bond and angle styles were used to include the flexibility. I have also tested this model before and it was running well without errors (or "obvious" errors).


On Thu, Apr 12, 2018 at 6:47 PM, Axel Kohlmeyer <akohlmey@...24...> wrote:
On Thu, Apr 12, 2018 at 12:13 AM, Pengyu Huang <> wrote:


>> On Wed, Apr 11, 2018 at 1:40 PM, Pengyu Huang <> wrote:
>> > Thank you very much, Axel, for your suggestions.
>> >
>> > I thought by defaults the bond, angle, dihedral and improper forces are
>> > calculated at the innermost timestep, and the multi-cut off setups are
>> > for
>> > the pair forces calculation, as the documents says " If not specified,
>> > the
>> > defaults are that bond forces are computed at level 1 (innermost loop),
>> > angle forces are computed where bond forces are, dihedral forces are
>> > computed where angle forces are, improper forces are computed where
>> > dihedral
>> > forces are, pair forces are computed at the outermost level, and kspace
>> > forces are computed where pair forces are.  " Thanks for pointing out
>> > this,
>> > I will double check the setup.

yes, but even though there are multiple options available, you do not
have to use them all.
for things that are "tricky" i prefer to not rely on defaults, but
make things explicit.

>> > Also thanks for your suggestions for the co2. I also want to model co2
>> > with
>> > flexible bonds and angle, so in this case I do not need a rigid
>> > integrator and using r-RESPA might help?

there is a problem, though.
an angle potential for a linear molecule has a problem for its
minimum, since the direction of the forces is not well defined. most
implementations will likely error out or produce invalid numbers.
have you researched whether there is an angle style that could be used
for this and whether this is available in LAMMPS?


>> >
>> > Regards,
>> > Pengyu

Dr. Axel Kohlmeyer  akohlmey@...43...4...
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.