Hi, everyone, I have a question about the reduced density in lj units.
In lj units, density = mass/volume, where rho* = rho sigma^dim, so if the density is 4.2e3 kg/m3, the diameter of particles is 2e-8 m, so the reduced density is 3.36e-20 kg. It looks weird. So i am not sure whether the ruduced progress is right in lammps. May be rho* should equal to rho sigma^dim /m. Can you give me some suggestions? Best wishes!
Don’t use reduced units if you want real parameters.
Hi, Axel, Thanks very much. I used the lennard jones potential in my brownian dymaics simulation. Can i use the real units in my simulations. Best wishes!
Hi, Axel, Thanks very much. I used the lennard jones potential in my
brownian dymaics simulation. Can i use the real units in my simulations.
you can do correct MD simulations in *any* set of units for as long as
all you input is consistent. that goes for your brownian dynamics just
as well. LAMMPS doesn't care; it will run the computations you ask
for. however, it is not always obvious to people that there are
connections between units. for example, you can choose energy, length
and mass, but that determines the unit of time.
apart from those general consideration, i would also like to caution
that the LJ potential is a rather soft interaction corresponding to
the softness of atoms and thus may not be that good a representation
of larger particles comprised of multiple atoms.
axel.
apart from those general consideration, i would also like to caution
that the LJ potential is a rather soft interaction corresponding to
the softness of atoms and thus may not be that good a representation
of larger particles comprised of multiple atoms.
Axel, thanks very much for your caution. I want to study the sedimentation process of nanoparticles by brownian dynamics simulation. And i need to consider the particle-particle interactions, if the LJ potential is not suitable for my situation, can you give me some suggestions. My model includes 10000 titanium dioxide nanoparticles, which diameters are all of 20 nm. Best wishes!
I suggest you find a paper in the literature that
has modeled a system like this and see what they
used, then how to mimic their model in LAMMPS.
Presumably you want to treat these as large,
coarse-grained single particles. LAMMPS has
many CG options, e.g. see the COLLOID package.
But to use the coarse-grained potentials, you
need to know what you are doing. The literature
is the best place to start.
Steve
Hi, Steve, thanks very much! Best wishes!