hi,everyone, i want to do aggregation process of nanoparticles by brownian dynamis in lammps, but i don’t know which commonds can be used to compute the number density of aggregates or the zeroth moment of aggregates. can you tell me if you kown? thanks very much!

For number density, you can look at fix ave/spatial which

can calculate spatially varying densities.

Zeroeth moment of what?

Steve

I believe by zeroth moment lujing just means the zeroth moment of the n-particle velocity distribution, i.e. the number density. Correct me if I’m wrong Lujing, but I believe you are looking for the number density of size classes. That is the number density of aggregates with k-particles. A former group member of mine looked at this exact problem if you are interested. (http://pubs.acs.org/doi/abs/10.1021/ie0711168 & http://pubs.acs.org/doi/abs/10.1021/ie3013715)

I will note that this is VERY easy to do with some simple post processing, as it depends only upon positions even if you use an energy criterion. But I guess you could also utilize dynamic groups somehow (here you would somehow have to identify chains of atoms, i.e. loop over all possible neighbors to see which particles have common neighbors) alongside fix ave/spatial. If it’s a homogeneous problem you just have to track the number of particles in your k-particle aggregate group and you can get the number density from there.