Dear QE users and developers, I calculate the energy using pw.x of GeTe in non-equilibrium positions and unit-cell. I get the following results:
"highest occupied, lowest unoccupied level (ev): 8.7256 7.626." I know that the material is a metal or semi-metal. The same thing happens with bismuth (in A7 structure) which is a semi-metal. I understand that this kind of calculations should be done with smearing and I read in previous messages by Paolo that it is known to happen in semi-metals and relates to the band-gap problem. I know the band-gap problem in DFT but I do not understand why a level which is lower in energy than the highest occupied level will not be occupied, and instead a higher level is occupied. I would expect that the calculation will not converge but I do not understand why it converges to the wrong state. Is it similar to the Janak theorem and fractional occupation in the Fe atom? The relevant levels for GeTe are: k = 0.0000 0.0000-0.8124 ( 1520 PWs) bands (ev): -17.0056 -17.0056 -16.9992 -16.9979 -16.9979 -3.7630 -1.5570 7.1574 7.1574 8.7256 8.7360 8.7360 9.2246 16.8372 16.8922 17.9505 17.9505 18.5818 18.5818 23.8031 occupation numbers 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 k = 0.1861-0.8594-0.2708 ( 1512 PWs) bands (ev): -17.0067 -17.0055 -16.9990 -16.9971 -16.9963 -3.3095 -1.0166 5.5826 5.8078 6.6930 7.6261 9.8147 9.9726 16.4111 16.5968 17.8171 17.8592 21.5515 21.7205 23.8798 occupation numbers 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 1.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 Uri Argaman Ben-Gurion University Israel
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