[DFTB-Plus-User] TDDFTB excitation window and OS filter

Benjamin Hourahine benjamin.hourahine at strath.ac.uk
Fri Oct 25 11:20:03 CEST 2019

Hello Fahri,

probably the manual needs some clarification. The energy window sets the minimum energy range for states to be included, the dipole window selects from all of the remaining unused single particle transitions above that window.



On 25/10/2019 09:58, Fahri Alkan wrote:
Hello all,
I am using DFTB+ to calculate the absorption spectra for very large systems. For such systems, one often needs to employ energy window (EW) and oscillator strength (OS) filter approximations to reduce the size of one-particle transition space. However, I believe there is a bug in the code when you invoke both of these filters. For a test system (Ag55 cluster), SPX.DAT shows 58286 transitions without any filter. When I apply 10^-3 OS filter alone, this number reduces to 14260. When I apply 0.1 au EW alone (with 100 Nr of excitations), one-particle transition space reduces to only 1759. If I use them together, what I expect reading from the manual is that one-particle transition space should reduce from 1759 to further some number as a result of OS filter. However, SPX.DAT shows 15549 excitations! (Even larger than the both numbers I get from filters alone). I am using the compiled binary version of DFTB-19.1. I haven't encounter any other problems with the program. My excitation block in the input is as follows:
ExcitedState = Casida {
 OscillatorWindow = 0.00100000000000000
 EnergyWindow = 0.10000000000000000
Is this a bug? Any comments on this will be appropriated greatly.

Asst. Prof. Fahri Alkan
Department of Material Science & Nanotechnology Engineering
Abdullah Gül University
Kayseri, Turkey
Office: BA102
Email: fahri.alkan at agu.edu.tr<mailto:fahri.alkan at agu.edu.tr>

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