Re: [lammps-users] Simulation of ellipsoids with dipoles

Dear Soumik,

A system of ellipsoids decorated with dipoles can indeed be simulated with the MOLC model. Luckily for you, the code works straight away. I recommend you to compile and use Matteo Ricci’s fork of Lammps on his github page. To use MOLC, compile LAMMPS with these options:
make yes-asphere yes-kspace yes-molecule yes-rigid # and more, if you need, such as yes-misc.
make yes-user-molc # Do this separately, as it will overwrite some files.
make your-architecture.

As Andrew pointed out, the aim is to merge our user package with the official Lammps distribution one day, but Matteo and myself are transitioning out of academia and this is a treacherous path! But don’t worry, we’ll get there, eventually.

I have prepared the MOLC force field definition of a single particle using the powerful Lammps-Template format, to be compiled with Moltemplate. Courtesy of Andrew Jewett! Check the parameters: the MOLC model uses a novel “off-centre” style for Coulomb and long-range electrostatics. This style adds mass-less point charges to ellipsoids. It works with the atom style “hybrid molecular ellipsoid” and “pair_style hybrid/overlay gayberne coul/long/offcentre”. You can compile the attached example with the command: -atomstyle “hybrid molecular ellipsoid” -molc

and run the input with:
lmp_30Oct19 -in

In the example you can chose between the good Langevin thermostat and a modified version of the Berendsen thermostat that works with aspherical particles. Alex, don’t be mad at us for promoting a thermostat which is know not to sample the canonical ensemble. The reason for having this thermostat is that velocity rescaling is a very robust method to thermalise complex systems, for instance a sample which has been built by putting together different simulations. The Berendsen thermostat is also very good for non-equilibrium simulations, e.g. the ballistic deposition of molecules over a surface, where you want to maintain the linear velocity and direction of the incoming molecule.

I hope this helps.
Good luck with your project.
Otello (2.24 KB) (789 Bytes)