Hi Everyone,
  I am James Johns from the University of Minnesota Chemistry Department.
I was trying to assign the modes in an experimental Raman spectrum by
comparison to calculations using symmetry and the predicted off-resonance
intensity (the material contains Mo and Te). The intensities that I
calculated seemed to be nonsense, so I tried looking at two simpler
systems, monolayer MoS2 and monolayer MoTe2.  When I calculate the Raman
intensities for MoS2, I get reasonable agreement with experiment (two
primary peaks, and E1 and A1, with similar intensities (A 2:1 ratio).  When
I swap to MoTe2, which has a similar first order Raman spectrum (2 peaks, 1
E1 and one A1 with similar intensity) I see that the symmetries are
correct, but the A1 mode is much more intense than the E1 pair (816 A^4/amu
vs 8 A^4/amu).   I thought his might be an issue with the Te
pseudopotential, so I tried two others (a Troullier-Martin and a
Hartwigsen-Goedeker-Hutter pseudopotential) and while the numbers changed,
the pattern didn't.
When I try to calculate the Raman intensities for my actual system, I
always see a similar trend where one mode is calculated to be vastly more
intense than the others.  I've copied the output of my dynmat input files
and the input files  for pw.x, ph.x, and dynmat.x below, but I wanted to
ask if anyone had any thoughts on why the LDA MoS2 intensity would be
approximately correct, but not MoTe2?

Thanks,
James Johns



MoTe2 Dynmat Output::


# mode   [cm-1]    [THz]      IR          Raman   depol.fact
    1     -0.00   -0.0000    0.0000         5.7100    0.7500
    2     -0.00   -0.0000    0.0000         5.7662    0.7500
    3      0.00    0.0000    0.0000         0.0562    0.7500
    4    119.78    3.5908    0.0000         0.5311    0.7500
    5    119.78    3.5908    0.0000         0.5311    0.7500
    6    174.02    5.2171    0.0000       816.7296    0.1155
    7    239.25    7.1726    5.0484         8.2978    0.7500
    8    239.25    7.1726    5.0484         8.2978    0.7500
    9    296.36    8.8846    0.0096         0.0000    0.1201


MoS2 Dynmat Output:

# mode   [cm-1]    [THz]      IR          Raman   depol.fact
    1     -0.00   -0.0000    0.0000         0.4655    0.7500
    2      0.00    0.0000    0.0000         0.0026    0.7500
    3      0.00    0.0000    0.0000         0.4645    0.7500
    4    287.40    8.6159    0.0000         0.2081    0.7500
    5    287.40    8.6159    0.0000         0.2081    0.7500
    6    390.61   11.7103    1.4530        73.6968    0.7500
    7    390.61   11.7103    1.4530        73.6968    0.7500
    8    406.95   12.2000    0.0000       461.7732    0.1076
    9    474.79   14.2337    0.0043         0.0000    0.1812
#######################################################
#######################################################

Input Files for MoS2
PW.X Input
 &control
     calculation= 'relax'
     nstep = 75
     etot_conv_thr= 1.0d-7
     forc_conv_thr= 1.0d-6
     prefix='MoS2.PBE'
     outdir='/home/johnsj/jjohns/MoS2_Phonon'
     pseudo_dir='/home/johnsj/jjohns/Psuedo/PSEUDOPOTENTIALS_NC'
     !tefield=.true.,
     !dipfield=.true.,
/
 &system
    ibrav= 4, celldm(1)=5.95799552 , celldm(3)=14.5844  nat= 3, ntyp=2,
nbnd=50,
    ecutwfc=60.0,
    occupations='fixed'
    !smearing='gauss'
    !degauss=0.01
    !vdw_corr= 'ts'
    !edir=3
    !emaxpos = 0.05
    !eopreg  =0.1
    !eamp=0
    !nspin=2
    !starting_magnetization(2)=0.5
    !input_dft='HSE'
    !nqx1=1, nqx2=1, nqx3=1
/
 &electrons
/
 &ions
/
 &cell
 !cell_dofree='2Dxy'
/

ATOMIC_SPECIES
 S 32.065  S.pz-n-nc.UPF
 Mo 95.94  Mo.pz-n-nc.UPF

ATOMIC_POSITIONS crystal
S 1/3 2/3 0.4642
Mo 2/3 1/3 0.5
S 1/3 2/3 0.5358

K_POINTS automatic
15 15  1 0 0 0




PH.X Input
phonons of MoS2 at Gamma
  &inputph
  tr2_ph=1.0d-14
  prefix='MoS2.PBE'
  outdir='/home/johnsj/jjohns/MoS2_Phonon'
  fildyn='MoS2.dynG'
  lraman=.true.
  asr=.true.
  epsil=.true.
  verbosity='high',
  /
0.0 0.0 0.0


Dynmat.x Input
 &input
fildyn='MoS2.dynG'
asr='crystal'
q=0.0 0.0 0.0
filxsf='MoS2.xsf'
/
#####################################################
#####################################################

Input Files for MoTe2

 &control
     calculation= 'relax'
     nstep = 75
     etot_conv_thr= 1.0d-7
     forc_conv_thr= 1.0d-6
     prefix='MoTe2.PBE'
     outdir='/home/johnsj/jjohns/MoS2_Phonon'
     pseudo_dir='/home/johnsj/jjohns/Psuedo/PSEUDOPOTENTIALS_NC'
     !tefield=.true.,
     !dipfield=.true.,
/
 &system
    ibrav= 4, celldm(1)=6.64030863 , celldm(3)=14.5844  nat= 3, ntyp=2,
nbnd=50,
    ecutwfc=60.0,
    occupations='fixed'
 /
 &electrons
/
 &ions
/
 &cell
 !cell_dofree='2Dxy'
/

ATOMIC_SPECIES
 Te 127.6  Te.pz-n-nc.UPF
 Mo 95.94  Mo.pz-n-nc.UPF

ATOMIC_POSITIONS crystal
Te 1/3 2/3 0.4642
Mo 2/3 1/3 0.5
Te 1/3 2/3 0.5358

K_POINTS automatic
15 15  1 0 0 0

PH.X Input
  phonons of MoTe2 at Gamma
  &inputph
  tr2_ph=1.0d-14
  prefix='MoTe2.PBE'
  outdir='/home/johnsj/jjohns/MoS2_Phonon'
  fildyn='MoTe2.dynG'
  lraman=.true.
  asr=.true.
  epsil=.true.
  verbosity='high',
  /
0.0 0.0 0.0

DYNMAT.X Input
 &input
fildyn='MoTe2.dynG'
asr='crystal'
q=0.0 0.0 0.0
filxsf='MoTe2.xsf'
/
################################################
################################################



-- 
James E. Johns
Assistant Professor
Department of Chemistry
University of Minnesota
207 Pleasant St.
Minneapolis, MN 55455
http://www.chem.umn.edu/groups/johns/index.html

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