compute charge flux

Dear LAMMPS users,

I’m trying to calculate thermal conductivity of uranium dioxide using the Green-Kubo formalism. Uranium dioxide is the two-component ionic system. There are two independent local macroscopic fluxes: heat flux Jq and electric (ionic, charge) flux Jz. Macroscopic coefficients of transport equations can be expressed in terms of microscopic time correlation functions of the dynamical variables Jz and Jq, representing the total fluxes of charge and heat in the system using Green-Kubo relations (M.J. Gillan, Phys. Scr. T39 (1991) 362–366.). Proceeding to thermal conductivity calculation, it was necessary to compute Jz and transport coefficients Lqq, Lqz, Lzz.

But compute heat/flux command calculate only heat flux Jq and respectively only Lqq.

Jz =1/V ∑zivi

Here V is volume, zi and vi are charge and velocity of ith particle.

I haven’t found a suitable compute command for Jz in compute styles on site.
How can I calculate Jz using lammps? Write a new compute style?

Any comment or suggestion would be highly appreciated.
Thank you.

I don't know. Can you relate the diffusoin
coeff (see the compute msd command) to
the flux? If not, you probably have to
post-process that quantity, by counting
how many charges cross a plane per unit
time. You could write a fix to monitor
that, but no one has done it.