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[lammps-users] Disagreement between compute temp/region and fix ave/chunk temp
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[lammps-users] Disagreement between compute temp/region and fix ave/chunk temp


From: Xiaoyu Wang <xwang181@...5818...>
Date: Fri, 25 May 2018 15:27:23 -0500

Dear all,

I am trying to simulate a non-equilibrium system to measure the thermo conductivity. Our system has two hot copper plates and one cold plate in the middle and between each of them is filled with water. We use eam for copper, SPC/e for water and lj for cross term. Since we are interested in local temperature in the system, I copied the idea in the examples by using fix Langevin. Here is my thermostat part.

compute Thot1   all temp/region hot1
compute Thot2   all temp/region hot2
compute Tcold   all temp/region cold
fix             1 all nve
fix hot1 all langevin ${thi} ${thi} 1.0 557667 tally yes
fix hot2 all langevin ${thi} ${thi} 1.0 59804 tally yes
fix cold all langevin ${tlo} ${tlo} 1.0 287859 tally yes
fix_modify  hot1 temp Thot1
fix_modify  hot2 temp Thot2
fix_modify  cold temp Tcold

Then I used several compute commands.

compute ke all ke/atom
variable    temp1    atom    c_ke/1.5
compute pencils all chunk/atom bin/2d x lower 0.5 z lower 0.5
fix     2 all ave/chunk 1000 10 10000 pencils v_temp1 ave running file temp1.profile
fix     5 all ave/chunk 1000 10 10000 pencils temp ave running file temp2.profile

What I found out is that the log file which shows the c_Thot1 c_Thot2 c_Tcold are right compared to our thermostat temperature. But either the c_ke or fix ave/chunk temp are not giving the right temperature for copper but seems to be right for water. Is it because of the DOF are different for copper and water?

Thanks in advance for any suggestions or ideas.

Andy