NGsBlkXd convergence troubles with RPA graphene EELS
Posted: Mon May 09, 2022 3:30 pm
Hi,
we (me and a colleague who actually does most of the Yambo/QE calculations) have tried to calculate EELS at a specific k-point, namely K, of several layer graphene.
We try to converge the calculation parameters first.
We already converged k-points, vacuum size to reasonable values for the computational resources currently available.
On top of that, we continued with FFTGvecs, bands BndsRnXd.
Unfortunately, NGsBlkXd (and FxcGRLc handled simultaneously) behaves surprisingly, see the plot attached.
We are not quite sure what is the cause of the "inflection" at the peak close to 14 eV as the value of the parameter seems to be rather large already.
The image represents bilayer graphene and the behavior is similar for all layer counts we have studied so far.
Please be aware that Yambo internally slightly shifts each value of 'NGsBlkXd' which can be verified by explicitly checking the output file(s).
Increasing value of the parameter 'NGsBlkXd' up to 9000 mRy (approximately 4500 mHa close to the expected likely-to-be "converged" value according to the link [http://www.attaccalite.com/reasonable-p ... culations/]) caused oscillations in the energy-loss dependence to appear in the case of a monolayer graphene.
Therefore, we tend to stick to smaller values that are approximately 1/10 of FFTGvecs.
I.e. they agree with the rule of thumb: NGsBlkXd should be much smaller than FFTGvecs.
The other parameters are as in the part of the input/output file.
We will appreciate any constructive suggestions.
Especially recommendation concerning value of NGsBlkXd.
Yambo version: 4.2.1 (revision 110)
Kind regards,
Martin Zouhar (Institute of Scientific Instruments, C.A.S., v.v.i.; the Czech Republic)
we (me and a colleague who actually does most of the Yambo/QE calculations) have tried to calculate EELS at a specific k-point, namely K, of several layer graphene.
We try to converge the calculation parameters first.
We already converged k-points, vacuum size to reasonable values for the computational resources currently available.
On top of that, we continued with FFTGvecs, bands BndsRnXd.
Unfortunately, NGsBlkXd (and FxcGRLc handled simultaneously) behaves surprisingly, see the plot attached.
We are not quite sure what is the cause of the "inflection" at the peak close to 14 eV as the value of the parameter seems to be rather large already.
The image represents bilayer graphene and the behavior is similar for all layer counts we have studied so far.
Please be aware that Yambo internally slightly shifts each value of 'NGsBlkXd' which can be verified by explicitly checking the output file(s).
Increasing value of the parameter 'NGsBlkXd' up to 9000 mRy (approximately 4500 mHa close to the expected likely-to-be "converged" value according to the link [http://www.attaccalite.com/reasonable-p ... culations/]) caused oscillations in the energy-loss dependence to appear in the case of a monolayer graphene.
Therefore, we tend to stick to smaller values that are approximately 1/10 of FFTGvecs.
I.e. they agree with the rule of thumb: NGsBlkXd should be much smaller than FFTGvecs.
The other parameters are as in the part of the input/output file.
We will appreciate any constructive suggestions.
Especially recommendation concerning value of NGsBlkXd.
Yambo version: 4.2.1 (revision 110)
Kind regards,
Martin Zouhar (Institute of Scientific Instruments, C.A.S., v.v.i.; the Czech Republic)