# Input File Description

## Program: bands.x / PWscf / Quantum Espresso

INTRODUCTION

&BANDS

prefix | outdir | filband | spin_component | lsigma | lp | filp | lsym | no_overlap | plot_2d | firstk | lastk

### INTRODUCTION

Purpose of bands.x:
Re-order bands, computes band-related properties. Currently,
re-ordering can be done with two different algorithms:
(a) by maximising the overlap with bands at previous k-point
(b) by computing symmetry properties of each wavefunction
Bands-related properties that can be computed are currently
(a) The expectation value of the spin operator on each spinor
wave-function (noncolinear case only)
(b) The expectation value of p

The input data can be read from standard input or from file using
command-line options "bands.x -i file-name" (same syntax as for pw.x)

Output files:
- file filband containing the band structure, in a format
suitable for plotting code "plotband.x"
- file "filband".rap (if lsym is .t.)  with symmetry information,
to be read by plotting code "plotband.x"
- if (lsigma(i)): file "filband".i, i=1,2,3, with expectation values
of the spin operator in the noncolinear case
- file "filband".gnu with bands in eV, directly plottable using gnuplot
- file filp with matrix elements of p

Structure of the input data:
============================

&BANDS
...
/


## Namelist: &BANDS

 prefix CHARACTER Default: 'pwscf' prefix of files saved by program pw.x 
 outdir CHARACTER Default: value of the ESPRESSO_TMPDIR environment variable if set; current directory ('./') otherwise directory containing the input data, i.e. the same as in pw.x 
 filband CHARACTER Default: 'bands.out' file name for band output (to be read by "plotband.x") 
spin_component INTEGER In the lsda case select: 1 = spin-up 2 = spin-down 
lsigma(i), i=1,3 LOGICAL If true computes expectation values of the spin operator on the spinor wave-functions (only in the noncollinear case), writes them to a file "filband".i, i=1,2,3 
 lp LOGICAL Default: .false. If .true. matrix elements of the momentum operator p between conduction and valence bands are computed and written to file specified in filp 
 filp CHARACTER Default: 'p_avg.dat' If lp is set to .true., file name for matrix elements of p 
 lsym LOGICAL Default: .true. If .true. the bands are classified according to the irreducible representations of the small group of k. A file "filband".rap with the same format of "filband" is written, for usage by "plotband.x" 
 no_overlap LOGICAL Default: .true. If .false., and if lsym is .false., writes the eigenvalues in the order that maximises overlap with the neighbor k-points 
 plot_2d LOGICAL Default: .false. If .true. writes the eigenvalues in the output file in a 2D format readable by gnuplot. Band ordering is not changed. Each band is written in a different file called filband.# with the format: xk, yk, energy xk, yk, energy .. .. .. energies are written in eV and xk in units 2\pi/a. 
 firstk, lastk INTEGER if lsym=.true. makes the symmetry analysis only for k points between firstk to lastk 
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