Extended Huckel Device calculation gets extremely slow

[yasheng]

Hi

I am doing some device calculations using extended huckel theory. It was pretty fast in the beginning, but it gets very slow after some time. See the energy below

|   0 E = -10007.2 dE =  2.372717e+00 dM =  3.881271e+00 dH =  2.766148e+00    |
|   1 E =  -9647.9 dE =  5.044531e-01 dM =  8.826795e-01 dH =  1.263772e+01    |
|   2 E = -9699.78 dE =  2.108909e-01 dM =  1.167843e+00 dH =  5.148475e+00    |
|   3 E = -9803.43 dE =  8.707716e-02 dM =  5.143593e-01 dH =  7.848367e-01    |
|   4 E = -9822.94 dE =  3.082800e-02 dM =  2.266662e-01 dH =  1.002323e+00    |
|   5 E = -9873.88 dE =  4.537150e-02 dM =  6.728930e-02 dH =  4.481365e-01    |
|   6 E = -9905.77 dE =  5.128498e-02 dM =  7.364029e-02 dH =  2.391064e-01    |
|   7 E = -9888.47 dE =  3.357228e-02 dM =  8.941489e-02 dH =  1.079357e-01    |
|   8 E = -9878.69 dE =  1.354342e-02 dM =  5.635861e-02 dH =  1.311752e-01    |
|   9 E = -9863.55 dE =  8.930520e-03 dM =  1.878326e-02 dH =  1.391255e-01    |
|  10 E = -9808.44 dE =  2.425624e-02 dM =  1.748760e-02 dH =  1.516485e-01    |
|  11 E = -9779.94 dE =  2.019184e-02 dM =  4.813811e-02 dH =  6.752169e-02    |
|  12 E = -9700.18 dE =  4.412686e-02 dM =  2.669891e-02 dH =  5.040059e-02    |
|  13 E = -9687.98 dE =  1.553101e-02 dM =  9.136254e-02 dH =  2.393973e-02    |
|  14 E = -9675.29 dE =  4.491408e-03 dM =  9.358001e-03 dH =  1.728568e-02    |
|  15 E = -9653.48 dE =  8.449555e-03 dM =  1.304811e-02 dH =  1.931539e-02    |
|  16 E = -9657.06 dE =  6.636468e-03 dM =  2.398464e-02 dH =  2.166887e-02    |
|  17 E = -9656.72 dE =  5.926826e-03 dM =  2.333166e-02 dH =  1.594946e-02    |
|  18 E = -9649.38 dE =  2.057189e-03 dM =  1.157775e-02 dH =  1.221886e-02    |
|  19 E =  -9649.8 dE =  9.569909e-04 dM =  8.755228e-03 dH =  1.364530e-02    |
|  20 E = -9650.44 dE =  4.131596e-04 dM =  2.258146e-03 dH =  8.320241e-03    |
|  21 E =  -9651.2 dE =  7.876470e-04 dM =  1.094355e-03 dH =  3.545779e-03    |
|  22 E = -9650.42 dE =  3.944362e-04 dM =  2.924421e-03 dH =  1.437835e-03    |
|  23 E = -9650.59 dE =  2.561794e-04 dM =  7.892831e-04 dH =  1.264300e-03    |
|  24 E = -9650.55 dE =  1.269612e-04 dM =  5.339099e-04 dH =  3.232002e-04    |
|  25 E = -9650.53 dE =  5.716055e-05 dM =  2.470325e-04 dH =  3.040669e-04    |
|  26 E = -9650.51 dE =  3.487375e-05 dM =  1.424110e-04 dH =  2.824968e-04    |
|  27 E =  -9650.5 dE =  3.046916e-05 dM =  9.223943e-05 dH =  1.448771e-04    |
|  28 E = -9650.49 dE =  4.055575e-05 dM =  1.324895e-04 dH =  1.066330e-04    |
|  29 E = -9650.49 dE =  3.746318e-05 dM =  1.685873e-04 dH =  4.697196e-05    |
|  30 E = -9650.49 dE =  7.948944e-06 dM =  3.468878e-05 dH =  1.020323e-04    |
|  31 E = -9650.48 dE =  7.207351e-06 dM =  2.625369e-05 dH =  7.815433e-05    |
|  32 E = -9650.47 dE =  9.508154e-06 dM =  2.164556e-05 dH =  3.843625e-05    |
|  33 E = -9650.47 dE =  1.048967e-05 dM =  5.130989e-05 dH =  3.154927e-05    |
|  34 E = -9650.47 dE =  5.263989e-06 dM =  2.555428e-05 dH =  1.370972e-05    |
|  35 E = -9650.47 dE =  1.897275e-06 dM =  1.002230e-05 dH =  1.006073e-05    |
|  36 E = -9650.48 dE =  9.147661e-07 dM =  5.963234e-06 dH =  7.529066e-06    |
|   0 E = -9972.47 dE =  2.396304e+00 dM =  3.882094e+00 dH =  3.051248e+00    |
|   1 E = -9664.55 dE =  5.067676e-01 dM =  8.794833e-01 dH =  1.228658e+01    |
|   2 E = -9735.68 dE =  2.127791e-01 dM =  1.179770e+00 dH =  5.818448e+00    |
|   3 E = -9873.96 dE =  1.056756e-01 dM =  5.449805e-01 dH =  9.256945e-01    |
|   4 E = -9900.72 dE =  4.139485e-02 dM =  2.481530e-01 dH =  1.154714e+00    |
|   5 E =  -9969.8 dE =  5.756637e-02 dM =  7.480533e-02 dH =  5.133595e-01    |
|   6 E = -9976.85 dE =  6.533643e-02 dM =  2.718134e-01 dH =  1.425417e-01    |
|   7 E = -9957.92 dE =  5.258978e-02 dM =  3.909658e-01 dH =  3.307109e-01    |
|   8 E = -9932.17 dE =  2.945179e-02 dM =  2.657950e-01 dH =  1.316867e-01    |
|   9 E = -9921.46 dE =  2.947370e-02 dM =  1.628053e-01 dH =  3.419604e-01    |
|  10 E = -9901.14 dE =  2.249100e-02 dM =  1.715336e-01 dH =  3.123765e-01    |
|  11 E = -9803.81 dE =  4.051056e-02 dM =  1.757609e-01 dH =  2.160042e-01    |
|  12 E = -9768.73 dE =  3.337533e-02 dM =  2.745907e-01 dH =  1.832847e-01    |
|  13 E = -9753.33 dE =  1.278105e-02 dM =  4.559303e-02 dH =  1.634954e-01    |
|  14 E = -9738.67 dE =  6.697541e-03 dM =  1.585258e-02 dH =  1.454397e-01    |
|  15 E = -9723.08 dE =  7.016223e-03 dM =  1.036462e-02 dH =  1.370453e-01    |
|  16 E =  -9710.5 dE =  8.441387e-03 dM =  1.674829e-02 dH =  1.278319e-01    |
|  17 E = -9711.24 dE =  1.103741e-02 dM =  3.331772e-02 dH =  9.347300e-02    |
|  18 E = -9710.51 dE =  1.430376e-02 dM =  5.546725e-02 dH =  3.832660e-02    |
|  19 E = -9705.64 dE =  1.043261e-02 dM =  5.771637e-02 dH =  2.055331e-02    |
|  20 E = -9704.09 dE =  1.517789e-03 dM =  7.250730e-03 dH =  1.422365e-02    |
|  21 E = -9704.25 dE =  6.092258e-04 dM =  4.573158e-03 dH =  8.808351e-03    |
|  22 E = -9703.45 dE =  5.262796e-04 dM =  3.780297e-03 dH =  1.060313e-02    |
|  23 E = -9702.27 dE =  7.224439e-04 dM =  2.300360e-03 dH =  7.719219e-03    |
|  24 E = -9701.98 dE =  9.999892e-04 dM =  6.052943e-03 dH =  1.106367e-03    |
|  25 E = -9701.86 dE =  1.693533e-04 dM =  6.722706e-04 dH =  8.378249e-04    |
|  26 E = -9701.77 dE =  2.337466e-04 dM =  8.310487e-04 dH =  7.761768e-04    |
|  27 E = -9701.79 dE =  1.500651e-04 dM =  1.362241e-03 dH =  1.280371e-03    |
|  28 E = -9701.73 dE =  2.289511e-04 dM =  1.569001e-03 dH =  2.215329e-04    |
|  29 E = -9701.74 dE =  5.490650e-05 dM =  3.694301e-04 dH =  1.984777e-04    |
|  30 E = -9701.74 dE =  2.505310e-05 dM =  1.249585e-04 dH =  1.533695e-04    |
|  31 E = -9701.75 dE =  1.905561e-05 dM =  5.049472e-05 dH =  1.232262e-04    |
|  32 E = -9701.74 dE =  2.630230e-05 dM =  1.329433e-04 dH =  5.317673e-05    |
|  33 E = -9701.74 dE =  1.562071e-05 dM =  5.118395e-05 dH =  5.218829e-05    |
|  34 E = -9701.75 dE =  1.263054e-05 dM =  7.951046e-05 dH =  6.459322e-05    |
|  35 E = -9701.75 dE =  7.727156e-06 dM =  3.191942e-05 dH =  3.316060e-05    |
|  36 E = -9701.75 dE =  5.153394e-06 dM =  3.623935e-05 dH =  1.594992e-05    |
|  37 E = -9701.75 dE =  2.231581e-06 dM =  1.423721e-05 dH =  1.180548e-05    |
|  38 E = -9701.75 dE =  1.755838e-06 dM =  5.739102e-06 dH =  6.154657e-06    |
|   0 E = -23987.4 dE =  2.594486e+00 dM =  3.881963e+00 dH =  1.677087e+01    |
|   1 E =   -24409 dE =  2.893981e-01 dM =  1.304877e+00 dH =  8.072611e+00    |
|   2 E = -24721.6 dE =  5.519631e-01 dM =  2.036661e+00 dH =  2.578159e+00    |
|   3 E = -24619.4 dE =  1.789553e-01 dM =  7.836281e-01 dH =  1.425827e+00    |


These highlighted steps are very slow. I noticed that there is the discontinuity in the energy here.

Let me know if you knw why this happens.

Thank you,
Yasheng

[zh]

Maybe your geometry structure has been changed dramatically during the optimization.

[yasheng]

No, that is device calculation. No geometry optimization is performed in this calculation.

[zh]

I see.

For a device calculation, the first step is the electrode calculation and then the whole device. The electrode calculation is very fast, but the calculation for the whole device is of course slow. And the energy of the electrode is smaller than that of whole device.

[yasheng]

Yes. That is true. But I expected that Extended Huckel method can be much faster than DFT calculations. But it is super slow at this point, and I cannot see that EH is faster than DFT.

[Daniele Stradi]

I guess the first two SCF cycles are the electrode calculations, and the "slow" one is the actual device. The device is probably 
larger than the two electrodes, so it makes sense that the device calculation is slower.

We could say something more if you send the input and output scripts of the calculation.

Regards,
Daniele.