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: [email protected] <[email protected]> on behalf of LEUNG Clarence <[email protected]> Sent: Monday, July 31, 2017 4:27 PM To: [email protected] 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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