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Re: [lammps-users] Issues with CNT Thermal Conductivity Calculations
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Re: [lammps-users] Issues with CNT Thermal Conductivity Calculations

From: Santosh Mogurampelly <vedhava@...24...>
Date: Tue, 29 Aug 2017 16:39:08 -0400

You should subtract the average of total energy from particle's total energy for the HCACF to decay to zero.

On Tue, Aug 29, 2017 at 3:06 PM, Daksha, Chaitanya Mrityunjay <daksha@...2437...> wrote:

Dear LAMMPS Users,


I am trying to calculate the thermal conductivity of a (10,10) CNT that is 5 nm in length using the Green-Kubo formalism.  I modified the liquid Argon LAMMPS thermal conductivity example for CNT.  First, I equilibrated the CNT structure at 300K, and then I ran the simulation to get the heat flux, heat current auto correlation function (HCACF) and thermal conductivity. To plot the HCACF, I averaged columns 4, 5, and 6 in the ‘J0Jt.dat’ file for every 1000 timesteps (which is my dump interval). 



Currently I am having two problems -

  1. The HCACF does not decay to zero. I have tried running the simulation for up to 1200 ps, but the HCACF still did not decay to zero. 
  2. The thermal conductivity value I attain differs based on the correlation length parameter I use in the ‘fix ave/correlate’ command.  Should the conductivity be independent of correlation length? If not, then how should I determine the appropriate correlation length?


I checked the LAMMPS email archive, but I was not able to find anything specific to my issues. Attached is the LAMMPS script, as well as other input data files. There is also a graph of the HCACF over time attached.


I would appreciate any insights as to why the HCACF does not decay to zero. 



Thank you,


Chad Daksha


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