[Pw_forum] How to get absorption coefficient
Timrov Iurii
iurii.timrov at epfl.ch
Mon Jul 31 17:33:43 CEST 2017
Dear Clarence,
Before continuing using turboTDDFT, I strongly recommend to read (at least) these two publications:
1. turboTDDFT - A code for the simulation of molecular spectra using the Liouville-Lanczos approach
to time-dependent density-functional perturbation theory Original Research Article
Authors: Osman Baris Malcioglu, Ralph Gebauer, Dario Rocca, Stefano Baroni
Source: Computer Physics Communications Volume: 182 Article Number: 1744 Published: APR 2011
2. turboTDDFT 2.0 - Hybrid functionals and new algorithms within time-dependent
density-functional perturbation theory
Authors: X. Ge, S. J. Binnie, D. Rocca, R. Gebauer, and S. Baroni
Source: Computer Physics Communications Volume: 185 Article Number: 2080 Published: MAR 2014
The full list of publications about the TDDFPT module of Quantum ESPRESSO can be found in qe/TDDFPT/README.
The 3x3 matrix chi_i_j is the polarizability (i and j run over the Cartesian components x, y, z, which in the plot_chi.dat file correspond to 1, 2, 3, respectively) - see Eq.(5) in the first reference mentioned above. In the file *.plot_chi.dat in the header you can see what is the meaning of each column, i.e.:
second column - energy \hbar \omega (Ry)
third column - real part of the polarizability Re(chi)
fourth column - imaginary part of the polarizability Im(chi)
In the same plot_chi.dat file, there is also the information (only if you performed Lanczos calculations along three Cartesian directions, i.e. ipol=4 - see the first reference above) about S(E) (second column) as a function of the energy (first column), which is the oscillator strength (the absorption coefficient). It is defined as (see the output file produced by turbo_spectrum.x, i.e. *.tddfpt_pp-out):
S(\hbar \omega) = 2m/( 3 \pi e^2 \hbar) \omega sum_j chi_j_j
HTH
Regards,
Iurii
--
Dr. Iurii Timrov
Postdoctoral Researcher
Swiss Federal Institute of Technology Lausanne (EPFL)
Laboratory of Theory and Simulation of Materials (THEOS)
CH-1015 Lausanne, Switzerland
+41 21 69 34 881
http://people.epfl.ch/265334
________________________________
From: pw_forum-bounces at pwscf.org <pw_forum-bounces at pwscf.org> on behalf of LEUNG Clarence <liangxy123 at hotmail.com>
Sent: Monday, July 31, 2017 4:27 PM
To: pw_forum at pwscf.org
Subject: [Pw_forum] How to get absorption coefficient
Dear QE users,
Now, I use the turbo_lanczos.x and turbo_spectrum to get the absorption spectrum.
I can get a plot_chi.dat file, as follow:
#Chi is reported as CHI_(i)_(j) \hbar \omega (Ry) Re(chi) (e^2*a_0^2/Ry) Im(chi) (e^2*a_0^2/Ry)
# S(E) satisfies the sum rule
chi_1_1= 0.000000000000000E+00 0.189914943334197E+04 0.000000000000000E+00
chi_2_1= 0.000000000000000E+00 -.949575309581559E+03 0.000000000000000E+00
chi_3_1= 0.000000000000000E+00 -.843216803071169E-03 0.000000000000000E+00
chi_1_2= 0.000000000000000E+00 -.949574977107089E+03 0.000000000000000E+00
chi_2_2= 0.000000000000000E+00 0.189915026381885E+04 0.000000000000000E+00
chi_3_2= 0.000000000000000E+00 0.110034487599961E-03 0.000000000000000E+00
chi_1_3= 0.000000000000000E+00 -.838178086194996E-03 0.000000000000000E+00
chi_2_3= 0.000000000000000E+00 0.109036445082823E-03 0.000000000000000E+00
chi_3_3= 0.000000000000000E+00 0.153710402502629E+03 0.000000000000000E+00
What is meaning of each row and how can I get the absorption coefficients?
Many thanks.
Clarence
City University of Hong Kong
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