1. Build up the 2D BN structure with your preferred atomistic model editor, such as VESTA, MS, and so on. Make note of the unit cell parameters and atomic coordinates.

2. Make a relax of the unit cell and atomic coordinates at the same time with a variable cell relax (vc-relax). Create your pwscf input file as follows:

############################BN.vc-relax.in############################

&CONTROL

calculation='vc-relax'

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 ='smearing',

degauss =1.0d-4,

smearing ='marzari-vanderbilt',

/

&ELECTRONS

electron_maxstep =1000,

conv_thr =1.0d-10,

mixing_mode = 'plain',

mixing_beta = 0.3d0,

scf_must_converge= .true.

/

&IONS

ion_dynamics='bfgs'

upscale=20.0

/

&CELL

press_conv_thr = 0.1D0

press = 0.D0

cell_dynamics = bfgs,

cell_dofree = '2Dxy'

cell_factor = 1.5D0

/

ATOMIC_SPECIES

B 10.81 B.pbe-n-van_ak.UPF

N 14.01 N.pbe-van_ak.UPF

CELL_PARAMETERS (angstrom)

2.4700000286         0.0000000000         0.0000000000

-1.2350000143         2.1390827721         0.0000000000

0.0000000000         0.0000000000        10.0000000000

ATOMIC_POSITIONS (crystal)

B 0.666666687         0.333333343         0.500000000

N 0.333333313         0.666666627         0.500000000

K_POINTS automatic

12 12 1 0 0 0

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

3. Launch the calculation with the following command:

$pw.x<BN.vc-relax.in>BN.vc-relax.out

4. Open the output file BN.vc-relax.out and look for the final coordinates as follows:

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

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

End final coordinates

A final scf calculation at the relaxedstructure.

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

5. Make a further relax calculation. Create your pwscf input file BN.relax.in as follows:

#########################BN.relax.in##############################

&CONTROL

calculation='relax'

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 = 'smearing',

degauss = 1.0d-4,

smearing = 'marzari-vanderbilt',

/

&ELECTRONS

electron_maxstep = 1000,

conv_thr = 1.0d-10,

mixing_mode = 'plain',

mixing_beta = 0.3d0,

scf_must_converge= .true.

/

&IONS

ion_dynamics='bfgs'

ion_positions = 'default'

/

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

12 12 1 0 0 0

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

6. Launch the calculation with the following command:

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

7. Open the output file BN.relax.out and look for the final coordinates as follows:

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

Begin final coordinates

ATOMIC_POSITIONS (crystal)

B       0.666666687   0.333333343   0.500000000

N       0.333333313   0.666666627   0.500000000

End final coordinates

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