Differences

This shows you the differences between two versions of the page.

--- band_structure [2012/11/30 10:16]
dani
+++ band_structure [2014/10/20 12:42]
@@ Line 1: / Line 1: @@
-===== The band structure =====
-To obtain the band structure of Si bulk of given lattice parameter we have to perform two steps.
-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
-for the lattice parameter ''alat = 5.5 Å'', than we have the **''fireball.in''** file containing:
-  &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 can determine the Fermi level from an 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).
-{{:si-bulk:fcc_brillouin.png?400|Brillouin zone FCC}}
-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?400|Si-bulk Band Structure}}
-===== 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:
-.0                   ! scale factor (leave 1.0)
-        2            ! list of atoms to analyze DOS
-                   ! number of energy steps
-  -18.0   0.05          ! initial energy, energy step
-                     ! leave untouched
-.0     0.0           ! leave untouched
-.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}}
-===== The bulk modulus =====
-  $ ls
-  Fdata  uno.bas  uno.kpts  uno.lvs  vol.sh
-  $ head uno.bas
-      0.000000      0.000000      0.000000
-      0.250000      0.250000      0.250000
-  $ head uno.kpts
-
-  -2.35619449         -2.35619449         -2.35619449        0.03125000
-  -3.92699081         -0.78539816         -0.78539816        0.03125000
-  -5.49778713          0.78539816          0.78539816        0.03125000
-  -7.06858347          2.35619449          2.35619449        0.03125000
-  -0.78539816         -3.92699081         -0.78539816        0.03125000
-  -2.35619449         -2.35619449          0.78539816        0.03125000
-  -3.92699081         -0.78539816          2.35619449        0.03125000
-  -5.49778713          0.78539816          3.92699081        0.03125000
-.78539816         -5.49778713          0.78539816        0.03125000
-  $ head  uno.lvs
-.5000    0.5000    0.0000
-.5000    0.0000    0.5000
-.0000    0.5000    0.5000
-The script to calculate the bulk modulus
-  $ cat vol.sh
-  #!/bin/bash
-  ##----- Parametros de control (el parametro de red tiene que encontrase entre ini fin  --------##
-  N=10
-  ini=5.0
-  fin=6.0
-  ##----------Funcion analisis para dos atomos/celda-----------------------------------------##
-  function analisis {
-  ETOT=$(grep 'ETOT' salida.out|cut -d'=' -f2)
-  sigma=$(grep sigma salida.out | cut -d'=' -f16 | tail -1)
-  charge=$(head -2 uno.bas | tail -1 | tr -s ' ' | cut -d' ' -f2)' -> '$(head -2 CHARGES | tail -1)
-  charge=$charge' ;'$(head -3 uno.bas | tail -1 | tr -s ' ' | cut -d' ' -f2)' -> '
-  charge=$charge$(tail -1 CHARGES)
-  echo $rescal$'\t'$ETOT$'\t'$sigma$'\t'$charge$'\t'>>salida
-  }
-  ##------------------------------------------------------------------------------------------##
-  function start {
-  rm -fr salida
-  for((i=0;i<=N;i++))
-  do
-  rescal=$(python -c "print '%.6f' % ($i*1.0*($fin-$ini)/$N+$ini)")
-  echo "&option
-  basisfile = uno.bas
-  lvsfile = uno.lvs
-  kptpreference = uno.kpts
-  rescal = $rescal
-  sigmatol = 0.000001
-  nstepf = 1
-  &end
-  &output
-  iwrtxyz = 1
-  &end" > fireball.in
-  ../progs/fireball.x > salida.out
-  analisis
-  done
-  }
-  ##----------------------------------1º start  ----------------------------------------------##
-  start
-  ##-----------------------------buscamos el minimo ------------------------------------------##
-  min=$(python -c "
-  x0 = []
-  y0 = []
-  for line in file(\"salida\"):
-     line = line.split()
-     x = line[0]
-     y = line[1]
-     x0.append(x)
-     y0.append(y)
-  j=0
-  for i in range(len(x0)):
-    if y0[j]< y0[i]:
-      j=i
-  print x0[j]")
-  cp salida borrar
-  rm -fr aux.py
-  ##----------------------------------2º start -----------------------------------------------##
-  N=40
-  d=0.4
-  ini=$(python -c "print '%.6f' % (1.0*($min-$d))")
-  fin=$(python -c "print '%.6f' % (1.0*($min+$d))")
-  start
-  mv salida Vol.dat
-  ##------------------------------------------------------------------------------------------##
-In the 1º start of the script "vol.sh" takes 10 points between 5-6:
-{{:bulk-si-10.png|}}
-In the 2º start of the script "vol.sh" takes 40 points between the minimum of the 1º start
-{{:si-bulk-40.png|}}
-The scripts uses the parameter rescal in fireball.in and unitary positions and lattice vectors with 2 atoms/cell
-to obtain the kpts points we used xeo:
-{{:xeo-menu-kpts.png|}}
-{{:xeo-kpts.png|}}
-The bulk mudulus can be calculed also with xeo (Utilities->Bulk modulus), in the in line command:
-  $ xeo -Bulk Vol.dat zincblende
-  E_min =     -214.35239    eV
-  a_min =        5.43719    angs
-  Volumen =       40.18518 ang**3
-  Bulk modulus =      100.79399  GPa

Nanosurf Lab

User Tools

Site Tools

Differences

Page Tools