Difference between revisions of "Calculating optical spectra including excitonic effects: a step-by-step guide"
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===Step 3: Bethe-Salpeter solver=== | ===Step 3: Bethe-Salpeter solver=== | ||
This is the final step in which you finally obtained the spectra. | This is the final step in which you finally obtained the spectra. | ||
Mathematically this implies to solve a large eigenvalue | Mathematically this implies to solve a large eigenvalue problem. | ||
Two main solvers are available in yambo | Two main solvers are available in yambo | ||
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It is clear that this makes a difference in the peak distribution and intensity. Note that beside a simple shift you can renormalise as well the bandwidth of the valence and conduction bands in KfnQP_E (respectively the third and second value). You can try as an exercise to set up a new calculation using e.g. 1.440000 | 1.200000 | 0.900000 | for KfnQP_E. | It is clear that this makes a difference in the peak distribution and intensity. Note that beside a simple shift you can renormalise as well the bandwidth of the valence and conduction bands in KfnQP_E (respectively the third and second value). You can try as an exercise to set up a new calculation using e.g. 1.440000 | 1.200000 | 0.900000 | for KfnQP_E. | ||
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=References = | =References = | ||
<references /> | <references /> | ||
Revision as of 14:29, 17 April 2017
WORK IN PROGRESS - by Myrta Grüning
This tutorial guides you through the workflow of a calculation of the optical spectrum of a given material by solving the Bethe-Salpeter equation. Specifically we will use bulk h-BN as an example.
Before starting, you need to obtain the tarballs for hBN. See instructions on the main tutorials page.
The target quantity in a Bethe-Salpeter calculation is the macroscopic dielectric matrix εM. The following quantities/steps are needed to obtain εM:
The optical absorption spectrum corresponds to ImεM(ω). Following this scheme we go through the flow of a calculation:
Step 1: Static screening
Use the SAVE folders that are already provided. For the CECAM tutorial, do:
$ cd YAMBO_TUTORIALS/hBN/YAMBO
Follow the Static screening module and then return to this tutorial Calculating optical spectra...
Step 2: Bethe-Salpeter kernel
Follow the module on Bethe-Salpeter kernel and return to this tutorial "Calculating optical spectra..."
Step 3: Bethe-Salpeter solver
This is the final step in which you finally obtained the spectra. Mathematically this implies to solve a large eigenvalue problem. Two main solvers are available in yambo
(1) diagonalization of the full Hamiltonian (diagonalization solver)
(2) subspace iterative Lanczos algorithm which by-pass diagonalization with the Haydock approach[1] (Lanczos-Haydock solver)
For (1) follow the module on Bethe-Salpeter solver: diagonalization then either return to this tutorial "Calculating optical spectra..." or follow the link to Bethe-Salpeter solver: Lanczos-Haydock for (2).
References
- ↑ R. Haydock, in Solid State Phys., 35 215 (1980) edited by H. Ehrenfest, F. Seitz, and D. Turnbull, Academic Press