# thermal conductivity of GNR

Dear LAMMPS users,
I want to calculate the thermal conductivity of GNR by using Green kubo method with Tersoff potentials.I read Lammps manual, but I have problem with values of Nevery,Nrepeat,Nfreq and run. I don’t know what numbers are true for these? I examined different values and I choose the answers,that were closer to the paper value.

for example :

"x=15nm ,y=75nm Nrepeat=15 Nevery=6 k= 2105.1143323283854[W/mK] @ 300 k

x=15nm ,y=100nm Nrepeat=15 Nevery=7 k=2288.6887319277112[W/mK] @ 300 k

x=15nm ,y=150nm Nrepeat=14 Nevery=8 k=2315.5698522367188[W/mK] @ 300 k

x=15nm ,y=200nm Nrepeat=15 Nevery=4 k=2426.6202233734834[W/mK] @ 300 k"

Nfreq=Nrepeat * Nevery

Are my answers and this method are correct?!

My other problem is the following command:

“fix NVT all nvt temp 300 300 10 drag 0.2”

I think my system is not well-equilibrated with 0.2, I don’t know what number is appropriate to an equilibrated system?
Step Temp E_pair E_mol TotEng Press
0 300 -555294.13 0 -553585.46 -15564.634
90 873.0662 -558540.11 0 -553567.49 -13005.801
180 1627.5528 -562842.08 0 -553572.21 -10375.94
270 2408.734 -567306.85 0 -553587.69 -7679.8525
360 3288.8099 -559851.34 0 -541119.62 -2225.3403
450 5840.0961 -536337.16 0 -503074.37 -2221.8055
540 7061.6031 -523881.46 0 -483661.46 -3585.4422
630 8096.6213 -510103.85 0 -463988.82 -3769.748
720 9548.0346 -494461.29 0 -440079.6 -2497.9576
810 10854.673 -476213.75 0 -414389.98 -1307.5393
900 12260.595 -457507.01 0 -387675.69 -867.5433
990 13461.92 -437880.61 0 -361207.04 213.88652
1080 14741.143 -417983.86 0 -334024.35 937.43781
1170 16050.084 -396617.97 0 -305203.28 1867.0342
1260 16712.179 -370901.47 0 -275715.75 1450.2545
1350 17124.382 -352352.21 0 -254818.76 1059.5574
1440 17216.119 -335606.94 0 -237550.98 1066.3467
1530 17490.808 -321313.83 0 -221693.36 1224.6084
1620 17769.98 -308808.75 0 -207598.23 1142.3581
1710 18048.016 -297460.47 0 -194666.37 1337.1905
1800 18459.213 -288318.68 0 -183182.58 1562.6309
1890 18703.843 -278421.98 0 -171892.56 1664.2334
1980 19174.121 -270805.58 0 -161597.65 1870.7035
2070 19348.828 -262116.21 0 -151913.23 1988.2112
2160 19718.11 -255208.24 0 -142901.97 2174.8123
2250 19956.608 -247785.84 0 -134121.19 2158.6532
2340 20226.97 -241180.38 0 -125975.86 2599.9998
2430 20357.6 -233993.11 0 -118044.57 2484.8901
2520 20675.435 -228916.01 0 -111157.21 2715.1069
2610 20713.141 -222384.58 0 -104411.03 2758.2957
2700 20956.702 -217334.34 0 -97973.569 2825.7003
2790 21172.359 -212245.3 0 -91656.232 2981.3462
2880 21274.669 -207015.32 0 -85843.537 3072.2799
2970 21428.881 -202416.04 0 -80365.92 3332.8301
3060 21735.475 -198805.44 0 -75009.093 3307.4744
3150 21901.18 -194542.44 0 -69802.3 3521.5806
3240 22056.965 -190559.38 0 -64931.953 3311.5795
3330 22219.862 -186852.37 0 -60297.154 3579.4524
3420 22372.919 -183957.32 0 -56530.349 3626.182
3510 22451.068 -180589.53 0 -52717.455 3842.8052
3600 22540.14 -177478.71 0 -49099.323 3931.2948
3690 22635.798 -174599.55 0 -45675.326 3909.1078
3780 22869.748 -172875.08 0 -42618.383 3950.5362
3870 22925.939 -170253.25 0 -39676.508 3901.7381
3960 22996.532 -167608.34 0 -36629.53 4053.2816
4050 23108.287 -165424.36 0 -33809.035 4083.4175
4140 23177.637 -163176.78 0 -31166.465 4228.6338
4230 23229.665 -161334.28 0 -29027.643 4269.0865
4320 23333.843 -159580.1 0 -26680.108 4365.2316
4410 23350.748 -157601.61 0 -24605.325 4256.9735
4500 23265.561 -155287.03 0 -22775.94 4377.7305
4590 23355.441 -154137.64 0 -21114.623 4440.6381
4680 23263.627 -152143.97 0 -19643.898 4413.1749
4770 23330.286 -151028.69 0 -18148.952 4510.4101
4860 23259.956 -149077.41 0 -16598.246 4528.1362
4950 23192.596 -147422.35 0 -15326.839 4673.9781
5040 23190.158 -146073.67 0 -13992.045 4605.4436
5130 23207.186 -144968.4 0 -12789.791 4578.5777
5220 23058.186 -143081.55 0 -11751.587 4603.3023
5310 23042.732 -142095.26 0 -10853.317 4615.5461
5400 22938.586 -140804.11 0 -10155.334 4707.9207
5490 22816.315 -139521.27 0 -9568.9009 4615.9391
5580 22775.113 -138660.93 0 -8943.228 4495.2673
5670 22773.982 -137945.34 0 -8234.0877 4573.8743
5760 22645.378 -136971.24 0 -7992.4586 4504.2785
5850 22479.853 -135725.62 0 -7689.605 4527.7111
5940 22367.594 -134735.35 0 -7338.7043 4554.7092
6030 22333.111 -134197.32 0 -6997.0756 4519.442
6120 22194.607 -133015.68 0 -6604.3038 4523.2135
6210 22165.214 -132297.76 0 -6053.7931 4458.9681
6300 22009.196 -130908.59 0 -5553.2387 4493.134
6390 21944.245 -130324.4 0 -5338.9829 4460.1994
6480 21881.118 -129606.88 0 -4981.0091 4513.541
6570 21715.148 -128447.72 0 -4767.1448 4450.4749
6660 21708.764 -128216.06 0 -4571.8446 4416.5099
6750 21578.404 -127228.09 0 -4326.3499 4428.2578
6840 21515.811 -126682.44 0 -4137.204 4286.6557
6930 21397.832 -125848.13 0 -3974.863 4188.4452
7020 21298 -125088.32 0 -3783.6476 4324.1663
7110 21261.865 -124844.47 0 -3745.6053 4431.8296
7200 21170.082 -124087.05 0 -3510.947 4316.0289
7290 21071.245 -123106.16 0 -3092.992 4297.1396
7380 21010.218 -122648.26 0 -2982.6731 4311.928
7470 20895.314 -122148.43 0 -3137.2991 4306.9994
7560 20778.135 -121478.5 0 -3134.7674 4149.4247
7650 20754.295 -121279.34 0 -3071.3909 4268.1958
7740 20700.953 -120805.01 0 -2900.8703 4177.7598
7830 20629.082 -120292.23 0 -2797.444 4185.6635
7920 20589.174 -120002.1 0 -2734.6074 4153.591
8000 20476.417 -119224 0 -2598.7314 4173.6613

Hi,

I think k values have no meaning anyway for such a system. First obtain stable GNR structure, make it run at constant temperature you need (not 20000 K), then try to calculate thermal condictivity. I guess the main problem is bad data file. Visualize your system.

If you’re not sure about drag value, you don’t have to set it.

Regards,
Oleg