# Fluid properties in a multi-component system

Greetings,

I have a system of methane/water mixture, and I have a lammps scripts that calculate the single-phase viscosity using the Green-Kubo relation. Can I use this GK relation to determine the viscosity of this new multi-component system? I mean, technically, the formula will give me a value, but is this reliable? Can I somehow revise the script such that it calculates the viscosities of water and methane separately?

Here is the lammps script to calculate viscosity:

variable pxy equal pxy
variable pxz equal pxz
variable pyz equal pyz
fix SS all ave/correlate \$s \$p \$d v_pxy v_pxz v_pyz type auto file S0St.dat ave running

#fix SS all ave/correlate/long \$s \$d v_pxy v_pxz v_pyz

variable scale equal {convert}/({kB}\$T)\$V*s*{dt}
variable v11 equal trap(f_SS[3]){scale} variable v22 equal trap(f_SS[4])*{scale}
variable v33 equal trap(f_SS[5])
\${scale}
variable vis equal (v_v11+v_v22+v_v33)/3.0

This is not really a question about LAMMPS and more a question about the science and thus not really on-topic for the LAMMPS categories (perhaps it is more suitable for “Science Talk”?).

As you have already seen, LAMMPS will execute any syntactically correct input and compute what it is programmed to compute. Whether that is meaningful is thus something you will have to sort out for yourself. Unless by chance somebody here has done exactly that kind of study and can thus give you a meaningful answer, you are probably best off searching the published literature about what people have done in such cases and how they have interpreted the results.

To my limited understanding of statistical mechanics, that seems like a very odd question. It sounds quite a bit like: “Can I have separate egg yolks and egg whites from a scrambled egg?”

1 Like

Thanks Axel. I will ask it in “Sciecne Talk” then.