[Pw_forum] Learning TDDFT calculation in Atomic label (CH4 molecule) using turbo_lanczos.x and turbo_davidson.x

[prem sen]

Dear Dr. Iurii Timrov,
                             Thanks for the reply.
"The two codes (Lanczos and Davidson) must give you the same absorption
spectrum (when both are converged)."

How to check the convergence for both the codes ??

I was checking the optical absorption spectra for CH4 molecule (using the
given example for the TDDFPT package) using both the code. They are not
matching with each other.


Also I was trying to do for Carbon-dimer.  In this case also, the spectrum
using both the codes are not matching with each other.  The input files are
given below.

I have checked the ecut & ecutfock convergence and also relaxed the
structure.

*For turbo_davidson.x ::*



*PW.X:*&CONTROL
  calculation  = "scf",
  restart_mode = "from_scratch"
  prefix       = "C2",
  pseudo_dir   = "../pseudo/",
  outdir       = "./tmp/",
/
&SYSTEM
  ibrav     = 0,
  nat       = 2,
  ntyp      = 1,
  ecutwfc   = 75,
  ecutfock  = 75,
  nosym     = .true.,
  input_dft = 'PBE0',
  x_gamma_extrapolation = .false.,
  exxdiv_treatment = 'vcut_spherical',
/
&ELECTRONS
  conv_thr    = 1.D-10,
  mixing_beta = 0.6,
  adaptive_thr = .true.,
/
CELL_PARAMETERS angstrom
10.0  0.0  0.0
 0.0 10.0  0.0
 0.0  0.0 10.0
ATOMIC_SPECIES
C  12.01  C.pbe-mt_gipaw.UPF
ATOMIC_POSITIONS (angstrom)
C        1.248029552   0.000000000   0.000000000
C        0.000000000   0.000000000   0.000000000
K_POINTS {Gamma}


*Turbo_davidson.x:*&lr_input
    prefix="C2",
    outdir="./tmp/",
/
&lr_dav
    ecutfock  = 75,
    num_eign=30,
    num_init=60,
    num_basis_max = 300,
    residue_conv_thr = 1.0E-4,
    start = 0.0
    finish = 1.0,
    step = 0.0005,
    broadening = 0.005,
    reference = 0.0,
    d0psi_rs = .true.,
    lshift_d0psi = .true.,
    p_nbnd_virt = 20
/


*For turbo_lanczos.x ::*

I used the same file for pw.x as given above.




*Turbo_lanczos.x:*&lr_input
    prefix="C2",
    outdir="./tmp/",
    restart_step=500,
/
&lr_control
    itermax=2000,
    ipol=4,
    ecutfock  = 75,
    pseudo_hermitian = .true.,
    d0psi_rs = .true.,
/




*Turbo_spectrum.x:*&lr_input
  prefix='C2',
  outdir="./tmp/",
  itermax0 = 410
  itermax  = 10000
  epsil=0.01
  start=0.0d0
  end=1.50d0
  increment=0.001d0
  ipol=4
/



Thanks & regards,
Prem Sen
Ph.D. Student,
IIT Bombay
*,*
Mumbai,India
*.*
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