[ase-users] vibration analysis with reaxff

[Claudio A. Perottoni]

Hi,

I am getting some strange results from vibration analysis of diamond with
reaxff-lg and reaxffc-2013. I created a diamond structure using

crystal('C', [(0,0,0)], spacegroup=227, cellpar=[a, a, a, 90, 90, 90])

and then converted it to the primitive cell, to speed up calculations and
facilitate comparison with the expected result (around 1333 cm-1).
Vibrational analysis was performed as

vib = Vibrations(atoms,delta=0.05)
vib.run()
vib.summary()

I have got the following results for different choices of interatomic
potentials (all calculations performed with LAMMPS):

airebo:
---------------------
  #    meV     cm^-1
---------------------
  0    0.0i      0.0i
  1    0.0       0.0
  2    0.0       0.0
  3  194.9    1571.7
  4  194.9    1571.7
  5  194.9    1571.7
---------------------

Tersoff:
---------------------
  #    meV     cm^-1
---------------------
  0    0.0i      0.0i
  1    0.0i      0.0i
  2    0.0       0.0
  3  194.6    1569.9
  4  194.6    1569.9
  5  194.6    1570.0
---------------------

lcbop:
---------------------
  #    meV     cm^-1
---------------------
  0    0.0i      0.0i
  1    0.0i      0.0i
  2    0.0       0.0
  3  146.6    1182.6
  4  146.6    1182.6
  5  146.6    1182.6
---------------------

reaxff-lg:
---------------------
  #    meV     cm^-1
---------------------
  0    0.0i      0.0i
  1    0.0i      0.0i
  2    0.0i      0.0i
  3  996.3    8035.7
  4  996.3    8035.7
  5  996.3    8035.7
---------------------

reaxffc-2013:
---------------------
  #    meV     cm^-1
---------------------
  0    0.0i      0.0i
  1    0.0       0.0
  2    0.0       0.0
  3  705.4    5689.8
  4  705.4    5689.8
  5  705.4    5689.8
---------------------

Has anyone got similar strange results when performing vibrational analysis
with reaxff/LAMMPS?

Regards,

Claudio

-- 

Claudio A. Perottoni

Universidade de Caxias do Sul
Rua Francisco Getúlio Vargas, 1130
95070-560 Caxias do Sul - RS - Brazil
http://www.researcherid.com/rid/B-8409-2008
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