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Update KKRSusc Quickstart Guide authored by Raffaele Aliberti's avatar Raffaele Aliberti
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title: KKRSusc Quickstart Guide
---
# Perform a KKRsusc calculation
In order to investigate spin-excitations via the KKRsusc program please
......@@ -55,8 +56,8 @@ and step 5 is finally performed with the KKRsusc program itself.
## Step 5: Calculate Self-energy and renormalized spectrum
To calculate the self-energy and renormalised spectrum of the system, a fitting procedure of the Green function to Padé polynomials is used, to facilitate the computational effort necessary to complete the calculation. For that, a set of kkrflex_* files similar to step 2 is needed, that contain the information for the host Green function over a large range of energies.
- Use the file [emesh.dat](emesh.dat), that describes an energy contour from $-0.3$ to $1.3$ Ry to run one iteration using the host code with the run flag KKRSUSC like in step 2.
To calculate the self-energy and renormalised spectrum of the system, a fitting procedure of the Green function to Padé polynomials is used, to facilitate the computational effort necessary to complete the calculation. For that, a set of `kkrflex_*` files similar to step 2 is needed, that contain the information for the host Green function over a large range of energies.
- Use the file [emesh.dat](emesh.dat), that describes an energy contour from $-0.3$ to $1.3$ Ry to run one iteration using the host code with the run flag `KKRSUSC` like in step 2.
- Similarly to the susceptibility calculation in step 4, two runs of the code are needed.
- Set `lfit= T` to instruct the code to run the fitting procedure and set the numerator polynomial degree `numd` and denominator degree `dend` to proper values, with $dend=numd +1$, to match the $1/\omega$ behaviour of the susceptibility in high frequencies. A typical range for `numd` is between 10-30, with the best fits usually in the region of 17-21.
- Set the bias voltage range (`vbiasmin`, `vbiasmax`) to match the frequency range defined by `omegamin`, `omegamax` and the corresponding parameters described in [newinpsusc.dat](newinpsusc.dat).
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