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band_structure [2009/11/25 22:20] jelen |
band_structure [2014/10/20 12:42] (current) |
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===== The band structure ===== | ===== The band structure ===== | ||
- | + | To obtain the band structure of Si bulk of given lattice parameter we have to perform two steps. | |
- | to calculate the band structure for given lattice parameter we need to achieve SCF solution. | + | First, 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 |
- | 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 we have the **''fireball.in''** file containing: |
- | for the lattice parameter ''alat = 5.5 Å'', than the **''fireball.in''** file contains: | + | |
&OPTION | &OPTION | ||
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where **''Si.bas''**, **''Si.lvs''** and **''Si.kpts''** files are identical as those used in previous [[bulk optimization|chapter]]. | 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 | + | Once we obtain the SCF solution, we can determine the Fermi level from an output file: |
mac135> grep "Fermi Level" $output_file | tail -1 | mac135> grep "Fermi Level" $output_file | tail -1 | ||
Fermi Level = -4.33045968490834 | 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). | + | 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|lgxg.kpts}}''** file (see also fig. 1). |
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multiplot> plot "ek.dat" using 1:7 with lines | multiplot> plot "ek.dat" using 1:7 with lines | ||
| | ||
- | {{:si-bulk:si-bulk.png|Si-bulk Band Structure}} | + | {{:si-bulk:si-bulk.png?400|Si-bulk Band Structure}} |
| | ||
+ | |||
===== DOS ===== | ===== DOS ===== | ||
+ | |||
+ | To plot Density of state, first, we have to achieve SCF solution in the same way as above (see previous [[band_structure|section]]). | ||
+ | Next we perform calculation with fixed SCF charges (switching on **''ifixcharge =1''**). The DOS calculation is initialized via variable **''iwrtdos''** in the section **''&OUTPUT''**. Hence, our **''fireball.in''** file looks like that: | ||
+ | |||
+ | &OPTION | ||
+ | basisfile = Si.bas | ||
+ | lvsfile = Si.lvs | ||
+ | kptpreference = Si.kpts | ||
+ | nstepf = 1 | ||
+ | ifixcharge = 1 | ||
+ | rescal = 5.5 | ||
+ | &END | ||
+ | &OUTPUT | ||
+ | iwrtdos = 1 | ||
+ | &END | ||
+ | |||
+ | In addition, **''dos.optional''** has to be presented in a working directory having following distance: | ||
+ | |||
+ | 1.0 ! scale factor (leave 1.0) | ||
+ | 1 2 ! list of atoms to analyze DOS | ||
+ | 360 ! number of energy steps | ||
+ | -18.0 0.05 ! initial energy, energy step | ||
+ | 0 ! leave untouched | ||
+ | 0.0 0.0 ! leave untouched | ||
+ | 0.05 ! imaginary part of Green function (controls energy level smearing) | ||
+ | |||
+ | After finishing a run, we obtain **''dens_001.dat''**,**''dens_002.dat''** including projected DOS on two Si atoms in the unit cell (including projected DOS onto individual shells of atoms). Additionally, there is a file **''dens_TOT.dat''** containing DOS. Here, a first column means energy and a second one DOS. | ||
+ | |||
+ | mac135> gnuplot | ||
+ | gnuplot> set xrange [0:1] | ||
+ | gnuplot> set yrange [-17:0] | ||
+ | gnuplot> set xlabel "DOS [arb. units]" | ||
+ | gnuplot> set ylabel "Energy [eV]" | ||
+ | gnuplot> plot "dens_TOT.dat" using 2:1 title 'Total DOS' with lines, \ | ||
+ | "dens_001.dat" using 11:1 title 'PDOS Si atom ' with lines | ||
+ | |||
+ | {{:si-bulk:pdos-si_bulk.png?400|DOS Si Bulk}} | ||
+ | |||
+ | |||
+ |