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Too Small Band Gap of Silicon (~0.65 eV) Calculated by VASP 已有1人参与
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Hello VASP users, I am a beginner in VASP. I tried to redo the Si example. BUT the band gap is ~0.65 eV, which is much smaller than the real value (1.17 eV). I am wondering what I am doing wrong. The below are the steps I have taken and corresponding inscripts. The pseudo-potential I used is from the folder /paw_pbe/Si. I also used the ultrasoft potential from the folder \pot\Si. But the band gap is the same. The results are similar to the one that presents on the website (https://wiki.alcf.anl.gov/wparker/index.php/Silicon) Could you please check my flow chart and see if I did something wrong? How can I get accurate energy calculated by VASP? Besides, I have another two questions for VASP usage. 1. I can get different Fermi energies from setp #2, #3.1 and #3.2. WHICH one is correct? The one from the SCF calculation? Should I use this value for the next steps (DOS and Band structure)? 2. What files should I copy to the folder of the next steps for continuation? Just CHGCAR and CHG, or CHGCAR, CHG and WAVECAR, or all the output files? If the ISTART = 0, does it mean I don't need to use any files from the previous step? =========================== Step #1: Structure Optimization. I initially set the lattice constants as 5.5 Angstrom (POSCAR). Then I did several ion steps to get the optimized structure (CONTCAR). INCAR file: System = Diamond Si ISTART = 0 ISMEAR = 1 SIGMA = 0.05 ENCUT = 300.0 NELM = 200 GGA = PE EDIFF = 1E-06 EDIFFG = -0.02 NPAR = 8 NSW = 50 IBRION = 2 ISIF = 3 ISYM = 1 KPOINTS file: K-Points 0 Monkhorst Pack 21 21 21 0 0 0 Output: CONTCAR, CHG, CHGCAR (for the next step #2) ===================================================== Step #2: SCF Calculation (Run self-consistently to get the charge density) I changed the CONTCAR file to POSCAR file for input structure. The k-point file is the same as above. INCAR file: System = Diamond Si ISTART = 0 ISMEAR = 0 SIGMA = 0.05 ENCUT = 300.0 NELM = 200 GGA = PE EDIFF = 1E-06 EDIFFG = -0.02 NPAR = 8 ISYM = 1 Output: CHG, CHGCAR, WAVECAR (for the next steps #3.1-DOS and #3.2-Band Structure) (Is it right? What files should I copy to the next step for continuation?) Fermi energy: 5.83091414 eV (read by the file DOSCAR. It wil be used for the next steps.) (We also can get different Fermi energies from step #3.1 and #3.2. Which one is the correct Fermi energy?) ================================================= Step #3.1: Non-SCF Calculation (DOS) I used the accurate charge density files from the previous step #2 for DOS.The k-point file is the same as above. INCAR file: System = Diamond Si ISTART = 1 ICHARG = 11 ISMEAR = -5 SIGMA = 0.05 ENCUT = 300.0 NELM = 200 GGA = PE EDIFF = 1E-06 EDIFFG = -0.02 NPAR = 8 ISYM = 1 Output: DOSCAR file --> DOS curve ================================================= Step #3.2: Non-SCF Calculation (Band Structure) I used the accurate charge density files from the previous step #2. The k-point file is different with a line mode. INCAR file: System = Diamond Si ISTART = 1 ICHARG = 11 ISMEAR = 0 SIGMA = 0.05 ENCUT = 300.0 NELM = 200 GGA = PE EDIFF = 1E-06 EDIFFG = -0.02 NPAR = 8 ISYM = 1 KPOINTS file: K-Points for FCC Bandstructure G-X-W-K-G-L-U-W-L-K|U-X 10 line reciprocal 0.000 0.000 0.000 ! G 0.000 0.500 0.500 ! X 0.000 0.500 0.500 ! X 0.250 0.750 0.500 ! W 0.250 0.750 0.500 ! W 0.375 0.750 0.375 ! K 0.375 0.750 0.375 ! K 0.000 0.000 0.000 ! G 0.000 0.000 0.000 ! G 0.500 0.500 0.500 ! L 0.500 0.500 0.500 ! L 0.250 0.625 0.625 ! U 0.250 0.625 0.625 ! U 0.250 0.750 0.500 ! W 0.250 0.750 0.500 ! W 0.500 0.500 0.500 ! L 0.500 0.500 0.500 ! L 0.375 0.750 0.375 ! K 0.250 0.625 0.625 ! U 0.000 0.500 0.500 ! X Output: EIGENVAL file --> Band Structure ================================ Thank you for your attention. If you have any suggestions or corrections, I will very appreciate that. Best, Wenpeng Zhu |
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小木虫: 金币+0.5, 给个红包，谢谢回帖
identation: 金币+1, 谢谢交流 2013-12-03 15:16:50
小木虫: 金币+0.5, 给个红包，谢谢回帖
identation: 金币+1, 谢谢交流 2013-12-03 15:16:50
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小木虫: 金币+0.5, 给个红包，谢谢回帖
小木虫: 金币+0.5, 给个红包，谢谢回帖
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