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Re: [lammps-users] special_bonds apply to Tersoff pair style
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Re: [lammps-users] special_bonds apply to Tersoff pair style

From: Axel Kohlmeyer <akohlmey@...24...>
Date: Wed, 20 Dec 2017 09:10:22 -0500

On Wed, Dec 20, 2017 at 8:55 AM, Jibao Lu <jibaolu2012@...29....> wrote:
Dear Sir/Madam,

I found that the weighting factors set by special_bonds ARE used by the pair style Tersoff, which compute many-body interactions. 
For example, for a system that uses Tersoff for a structure with lists of bonds, angles, dihedrals (for debuging purpose, the bonded interactions are set to zero by settin K = 0.0), seting "special_bonds lj 0.0 0.0 0.5 coul 0.0 0.0 0.5" will apply the factor 0.0 to the Tersoff interactions; If setting ""special_bonds lj 1.0 1.0 1.0 coul 1.0 1.0 1.0", the Tersoff interactions are calculated as if for the same structure but without list of bonds, angles, and dihedrals. 

Could you please check for that? Thank you!

​you are not correct. the weighting factors are *not* applied. it is very obvious from reading the source code.
however, if you set a scaling factor to 0.0, the affected pairs will be entirely removed from the neighbor list, which is the documented behavior and the reason why you will see LAMMPS print a warning when you apply a many-body potential with also having explicit bonded interactions defined in the topology (regardless of of their force constants).

all of this is expected and documented behavior.



I'm using lammps-11Aug17.

Best regards,

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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.