1. First we perform a non-self-consistent calculation (nscf) based on the results of the self-consistent calculation in the previous step. Denser k-point mesh are needed:

######################BN.scf.in###############################

&CONTROL

calculation='nscf'

title='BN'

prefix='BN'

restart_mode='from_scratch'

nstep=1000

outdir='./tmp'

pseudo_dir='./'

wf_collect=.true.

tstress=.true.

tprnfor=.true.

/

&SYSTEM

ibrav= 0

nat=2

ntyp=2

ecutwfc = 60.0,

ecutrho = 600.0,

input_DFT ='PBE',

occupations = 'tetrahedra',

degauss = 1.0d-4,

/

&ELECTRONS

electron_maxstep = 1000,

conv_thr = 1.0d-10,

mixing_mode = 'plain',

mixing_beta = 0.3d0,

scf_must_converge= .true.

/

ATOMIC_SPECIES

B 10.81 B.pbe-n-van_ak.UPF

N 14.01 N.pbe-van_ak.UPF

CELL_PARAMETERS (angstrom)

  2.511218514   0.000000000   0.000000000

 -1.255609257   2.174779027   0.000000000

  0.000000000   0.000000000  10.000000000

ATOMIC_POSITIONS (crystal)

B        0.666666687   0.333333343   0.500000000

N        0.333333313   0.666666627   0.500000000

K_POINTS automatic

24 24 1 0 0 0

###################################################################

2. Launch the nscf calculation:

$pw.x<BN.scf.in>BN.scf.out

3. Make eigenvalues readable in a suitable format.

##########################fs.in####################################

&fermi

outdir='./'

prefix='BN'

/

###################################################################

4. Launch the fs calculation:

$fs.x<BN.fs.in>BN.fs.out

5. The Fermi surface can be visualized with XCrySDen by opening with the file BN_fs.bxsf