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Re: [lammps-users] QMMM with lammps
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Re: [lammps-users] QMMM with lammps

From: Axel Kohlmeyer <akohlmey@...24...>
Date: Mon, 20 Nov 2017 06:49:45 -0500

On Mon, Nov 20, 2017 at 4:16 AM, daniele selli <daniele.selli@...7246...> wrote:
Dear All,

I would like to use lammps to perform QMMM calculations using our
own QM-MM interface.
In order to do that, we need lammps to handle external charges. This means
that at each MD step, the forces on the QM atoms due to the MM point charges are calculated, as well as the forces on the MM charges due to interaction with the QM atoms.

​this is a rather vague description and thus difficult to provide any specific advice.​
Does lammps allows to calculate forces on point charges?

​interaction with point charges is what all */coul/* styles do. again, because if your vague description, it is not possible to provide a specific answer.​
If yes, which is the command to do that?

​it is unlikely that you will be able to set this up without some C++ programming.
there are multiple ways, how LAMMPS is coupled to external programs.
- there is the generic QM/MM library in LAMMPS that currently couples LAMMPS to quantum espresso, where there is a driving code, which uses different MPI partitions and through that manages 2 copies of LAMMPS and 1 copy of quantum espresso and then a fix qmmm to communicate the information between the different partitions.
- there is the LATTE package, which couples LAMMPS to a tight-binding code, where LAMMPS is the driver and then the LATTE code is called through a library interface from fix latte
- there is the coupling of LAMMPS to the DFTB+ code, where the DFTB+ code is the driver and interaction with LAMMPS is handled through callback functions registered with fix external

i suggest you study those three examples and the related documentation and readme files. then identify which of those is closest to what you need and then copy/rename/adapt the corresponding code to your needs.



Thank you all for your willingness,

Daniele Selli

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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.