I’m trying to calculate thermal conductivity of a nanofluid using the direct method. So, I’m trying to understand the in.hex input file in the KAPPA example.
In the read me document under number (3) in.ehex, “dTemp = 0.770 from log file for average Temp difference between 2 regions”
From the logfile I average the v_tdiff column but it equals 0.763421241 not 0.770 as mentioned in read me. Also, I looked at the other input files it nevers comes to the stated value in the read me.
So, my question is dTemp = average v_tdiff indeed or am I doing something wrong?
As the README file says, dTemp in that case is the running average of v_tdiff. That means it is accumulated for every step, not just the steps where you get thermo output.
This is done by fix ave/time and thus the column that is relevant is the “f_ave” column, which - incidentally - has that result at the final step.
Please note that the example output are over 5 years old and thus may be subject to changes in the LAMMPS core code that can lead to different trajectories yet equivalent results. Please also see the comments in this page: https://docs.lammps.org/Errors_common.html
It should be common practice to run such simulations multiple times with different starting conditions (and usually longer trajectories) to get an assessment for the statistical convergence of the computed result. As you can see from the differences between results of the different methods, the convergence of the settings used is not very tight. But after all, this is just an example to demonstrate the procedure NOT to get highly accurate results.