Dear developers and users,
First of all, I followed the example on compute heat/flux page to study a single sheet of graphene without any problem. Then I'm trying to compute the heat flux in a system composed of a graphene sheet on a sio2 substrate in equilibrated constant energy ensemble. However, I found that the heat flux in this case is about several times larger than that case when there is only a single graphene sheet. This is unexpected because if Green-Kubo method is used based on such heat flux value, due to a large autocorrelation function, an unphysically large thermal conductivity value is resulted. I closely followed the example provided on the compute heat/flux page and I did define compute ke/atom etc. using the same group as used by compute heat/flux. I checked the formulation used to compute heat current, which is
J= sum e_i v_i + 0.5 sum (f_ij * ( v_i + v_j)) r_ij
I can correctly plot the phonon DOS, so I think the velocities are fine, and I cannot see why e_i, f_ij and r_ij could be wrong. So I'm thinking if there could be a bug when computing the heat flux in a inhomogeneous system like the one described here. I can post my input and other results if needed. Thanks!
The heat current I obtained for combined system (not divided by volume). For instance J_graphene_y is about 1000 rather than around 100~200
Step T_total T_graphene T_sio2 J_total_x J_total_y J_graphene_x J_graphene_y J_sio2_x J_sio2_y
980 306.39639 307.12495 306.26429 617.35114 -1044.5349 74.679789 -929.30782 542.67135 -115.22708
990 303.30044 293.0246 307.97336 465.86349 -1173.2185 61.494599 -951.29552 404.36889 -221.92303
1000 301.35906 284.70745 308.81584 243.9928 -1492.084 57.352149 -979.79229 186.64065 -512.29172
1010 301.05119 288.73513 306.61394 274.21896 -1619.9197 99.706495 -1006.6044 174.51247 -613.31525
1020 301.68731 297.34578 303.76705 334.78362 -1487.9385 179.08974 -1015.0053 155.69388 -472.93321
1030 302.48324 300.79699 303.40359 534.94672 -1218.0079 247.80235 -1011.7078 287.14437 -206.3001
1040 301.49924 298.45163 303.01366 625.72718 -972.88291 264.97314 -1028.5007 360.75403 55.61781
1050 302.3801 298.5795 304.22397 701.26153 -1075.2168 231.08803 -1080.6749 470.17351 5.4580833
1060 306.34253 304.64485 307.27023 860.98445 -1058.2901 184.32805 -1149.2712 676.6564 90.981065
1070 309.61732 306.94997 310.97056 910.03291 -918.57712 161.21415 -1197.1053 748.81877 278.52813
1080 307.01076 298.23791 311.0294 889.24083 -836.32682 162.17057 -1193.2289 727.07026 356.90206
1090 303.89042 288.36854 310.85526 613.77726 -1077.6778 159.67712 -1141.8684 454.10014 64.190661
1100 302.79404 289.6409 308.72351 227.62664 -1229.6045 134.10506 -1086.97 93.521584 -142.63447
The heat current I obtained for single graphene sheet for comparison
Step T_graphene J_graphene_x J_graphene_y
0 277.2783 -99.55638 -81.354693
10 292.16742 24.749244 -185.91829
20 294.96592 -10.440488 -163.69911
30 288.76916 -218.61152 -151.89496
40 288.98167 -105.2722 -155.36314
50 293.3518 -116.39535 -3.4446361
60 283.10224 -93.979776 -147.81794
70 302.96888 -58.062824 -233.84752
80 284.44289 -180.45572 -124.62181
90 297.89118 -137.1921 -99.936134
100 282.53282 -113.83959 -107.37939
110 294.81692 -148.54612 -82.443137
120 278.73482 -78.765497 -112.74231
Thanks,
Bo