[QE-users] Non-smooth tail in potential energy curve for non-metals

[Kevin Kayang]

Dear Quantum Espresso Community,

I am trying to perform DFT calculations with Van der Waals corrections on
non-metal dimers at different distances to obtain a potential energy curve.
In my results however, I noticed an unusual sharp jump in the tail of the
potential energy curve which I cannot explain for non metals dimers of
Carbon, Nitrogen and Silicon. Metallic dimers however did not exhibit such
behavior. What is the reason for such behavior? Could this be an inherent
problem with QE?

Please see below a sample of my input script and attached a copy of my
results for Nitrogen dimers.

&CONTROL
 calculation = 'scf' ,
 wf_collect = .true. ,
 outdir = './' ,
 pseudo_dir = './' ,
 prefix = 'n_dimer-df2_1.70' ,
 disk_io = 'none',
 /
 &SYSTEM
 ibrav     = 0,
 celldm(1)= 1.88972687,
 ntyp      = 1,
 nat       = 2,
 ecutwfc = 90,
 ecutrho = 900,
 nosym = .FALSE.
 input_dft = vdw-df2
 occupations = 'smearing',
 smearing = 'gauss',
 degauss = 0.0001,
 one_atom_occupations = .TRUE.,
 nspin = 2,
 starting_magnetization(1) = 1,
 starting_magnetization(2) = 1,

 /
 &ELECTRONS
 electron_maxstep = 1000,
 conv_thr = 1d-7,
 mixing_mode = 'plain',
 mixing_beta = 0.3,
 /
 &IONS
 /

 /
 &CELL
 /

CELL_PARAMETERS cubic
   20.000000000   0.0000000000   0.0000000000
   0.0000000000   20.000000000   0.0000000000
   0.0000000000   0.0000000000   20.000000000

ATOMIC_SPECIES
N 14.0067 N.pbe-n-kjpaw_psl.1.0.0.UPF

ATOMIC_POSITIONS { angstrom }
N      0.0 0.0 0.0
N      0.0 0.0 1.70

K_POINTS gamma

[image: pec.png]

Thank you in advance!

Kevin Kayang
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