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.
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:
moltemplate.sh -atomstyle “hybrid molecular ellipsoid” -molc annealing_01.lt
and run the input with:
lmp_30Oct19 -in annealing_01.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.
annealing_01.lt (2.24 KB)
ellipsoid.lt (789 Bytes)