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band_structure [2009/11/25 22:20] jelen |
band_structure [2014/10/20 12:42] |
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- | ===== The band structure ===== | ||
- | to calculate the band structure for given lattice parameter we need to achieve SCF solution. | ||
- | Therefore we run a standard bulk calculation as described in the previous [[bulk optimization|chapter]]. Let's calculate the band structure | ||
- | for the lattice parameter ''alat = 5.5 Å'', than the **''fireball.in''** file contains: | ||
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- | |||
- | &OPTION | ||
- | basisfile = Si.bas | ||
- | lvsfile = Si.lvs | ||
- | kptpreference = Si.kpts | ||
- | nstepf = 1 | ||
- | rescal = 5.5 | ||
- | &END | ||
- | |||
- | where **''Si.bas''**, **''Si.lvs''** and **''Si.kpts''** files are identical as those used in previous [[bulk optimization|chapter]]. | ||
- | Once we obtain the SCF solution, we determine the Fermi level from output file | ||
- | |||
- | mac135> grep "Fermi Level" $output_file | tail -1 | ||
- | Fermi Level = -4.33045968490834 | ||
- | |||
- | In next step, we run the ''FIREBALL'' code again, but now with fixed charges (**''ifixcharge = 1''**) and with a new set of k-points in desired high-symmetry directions in the first Brillouin zone. Remember we need having **''CHARGES''** file in a working directory for a restart. In this particular case,we have chosen a direction ''L-Γ-X-Γ'' stored in a **''lgxg.kpts''** file (see also fig. 1). | ||
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- | {{:si-bulk:fcc_brillouin.png?400|Brillouin zone FCC}} | ||
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- | |||
- | In addition, we have to write out a list of eigenvalues at each k-point switching on **''iwrteigen''** variable. Our input file **''fireball.in''** has following form now: | ||
- | |||
- | &OPTION | ||
- | basisfile = Si.bas | ||
- | lvsfile = Si.lvs | ||
- | kptpreference = lgxg.kpts | ||
- | nstepf = 1 | ||
- | ifixcharge = 1 | ||
- | rescal = 5.5 | ||
- | &END | ||
- | &OUTPUT | ||
- | iwrteigen = 1 | ||
- | &END | ||
- | |||
- | After the run, we obtain a file **''ek.dat''** appears in a working directory. This file contains at each line set of eigenvalues for given k-points ordered in ascending form. The Fermi level can | ||
- | Now we have all information to plot the band structure of the Si bulk. | ||
- | |||
- | mac135> gnuplot | ||
- | gnuplot> set xrange [0:300] | ||
- | gnuplot> set yrange [-17:0] | ||
- | gnuplot> set xlabel "k-points" | ||
- | gnuplot> set ylabel "Energy [eV]" | ||
- | gnuplot> set nokey | ||
- | gnuplot> set multiplot | ||
- | multiplot> plot "ek.dat" using 1:2 with lines | ||
- | multiplot> plot "ek.dat" using 1:3 with lines | ||
- | multiplot> plot "ek.dat" using 1:4 with lines | ||
- | multiplot> plot "ek.dat" using 1:5 with lines | ||
- | multiplot> plot "ek.dat" using 1:6 with lines | ||
- | multiplot> plot "ek.dat" using 1:7 with lines | ||
- | | ||
- | {{:si-bulk:si-bulk.png|Si-bulk Band Structure}} | ||
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- | ===== DOS ===== |