[QE-users] Reg- Absorption spectrum using TDDFPT (turbo_davidson.x, turbo_lanczos.x and epsilon.x)

[Vivek Christhunathan]

Dear QE users,

Greetings!!!

I am trying to find the absorption spectrum for the material 'TiO2'
supercell (2*1*1) which consists of 24 atoms. I tried a lot to find the
absorption spectrum by reading all the related threads from QE. I have
tried with all the methods such as turbo_davidson.x, turbo_lanczos.x and
epsilon.x. I can only succeed with the use of epsilon.x but I am unable to
get the same results for the turbo_davidson.x and turbo_lanczos.x. I would
like to know the reason behind this. And secondly to find an absorption
spectrum of the material does epsilon.x method gives accurate results when
compared with the other two?

Thirdly I have tried it for the Zn doped TiO2 supercell. This time all the
methods did not give a hand for my calculation. The input files are given
below. I would be very grateful if you help me out in this regard.

Please let me know if you need any further information. Looking forward to
hearing from you.

Thanks in advance.

# self-consistent calculation
&control
calculation = 'scf'
prefix = 'TiO2'
pseudo_dir = './'
outdir = './outTiO2'
!etot_conv_thr = 1e-5
forc_conv_thr = 1e-4
/
&system
ibrav = 0
celldm(1) = 14.113
nat = 24
ntyp = 2
ecutwfc = 80.0
ecutrho = 800
nbnd = 300
input_dft = 'pbe0'
/
&electrons
mixing_beta=0.3
conv_thr = 1.0d-8
diagonalization = 'david',
mixing_mode = 'plain',
/
&IONS
/
&cell
/
CELL_PARAMETERS (alat)
   1.000927809   0.000000000   0.000000000
   0.000000000   0.500440909   0.000000000
   0.000000000   0.000000000   1.235414320
ATOMIC_SPECIES
 Ti 47.867 Ti.upf
 O  16.00  O.upf
ATOMIC_POSITIONS (crystal)
Ti       0.000000000   0.000000000  -0.000006420
Ti       0.500000000   0.000000000  -0.000006418
Ti       0.250000017   0.500000000   0.499993602
Ti       0.750000015   0.500000000   0.499993602
Ti       0.000000000   0.500000000   0.250006398
Ti       0.500000000   0.500000000   0.250006394
Ti       0.250000016   0.000000000   0.750006426
Ti       0.750000016   0.000000000   0.750006426
O        0.000000000   0.000000000   0.212511476
O        0.500000000   0.000000000   0.212511476
O        0.250000011   0.500000000   0.712511501
O        0.750000021   0.500000000   0.712511501
O        0.000000000   0.500000000   0.462514694
O        0.500000000   0.500000000   0.462514705
O        0.250000019   0.000000000   0.962514709
O        0.750000013   0.000000000   0.962514709
O        0.250000008   0.000000000   0.537488518
O        0.750000024   0.000000000   0.537488518
O        0.000000000   0.500000000   0.037488489
O        0.500000000   0.500000000   0.037488487
O        0.250000019   0.500000000   0.287485309
O        0.750000013   0.500000000   0.287485309
O        0.000000000   0.000000000   0.787485317
O        0.500000000   0.000000000   0.787485307
K_POINTS gamma

# turbo_lanczos.x calculation
 &lr_input
prefix ='TiO2'
outdir ='./outTiO2'
!restart_step = 100,
!restart = .true.
/
&lr_control
itermax = 500
ipol = 1
!d0psi_rs = .true.
/
# turbo_spectrum.x calculation
&LR_INPUT
prefix = 'TiO2'
outdir = './outTiO2'
itermax0 = 500
itermax = 10000
extrapolation = 'osc'
epsil = 0.01
units = 1
start = 0.0
end = 4.0
increment = 0.01
ipol = 1
/
# turbo_davidson.x calculation
&lr_input
prefix = 'TiO2'
outdir = './outTiO2'
/
&lr_dav
!if_dft_spectrum = .false.
num_eign = 5
num_init = 10
num_basis_max = 90
residue_conv_thr = 1.0E-4
start = 0.0
finish = 3.50
step = 0.001
broadening = 0.004
reference = 0.3
/
  # turbo_spectrum.x calculation
&lr_input
prefix = 'TiO2'
outdir = './outTiO2'
td = 'davidson'
epsil = 0.004
start = 0.0d0
end = 3.5d0
increment = 0.001d0
eign_file = 'TiO2.eigen'
/

Kind Regards,

Vivek C


__________________________________

Vivek Christhunathan

PhD researcher

Mechanical Engineering

College of Engineering and Informatics

Room 2053

Alice Perry Engineering Building

National University of Ireland Galway

Ireland
E-mail: v.christhunathan1 at nuigalway.ie
Phone: +353 899811181, +91 9600752742
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