Transferred momenta and different LongDrXd orientation
Posted: Tue Oct 04, 2022 5:25 pm
Dear Yambo developers and more experienced users,
we have calculated alpha (which should represent EELS) for a monolayer graphene.
We intend to calculate at q-points outside of the 1st BZ (Brillouin zone) and also separately calculate both q-parallel (in-plane) and q-perpendicular incidence.
We experimented with increasing number of q-points with different q_z coordinates (real-space z-axis is perpendicular to the graphene sheet).
1) Negative alpha outside of the 1st BZ:
Strangely enough, our results with interaction (local field effects), column 2 ('ALPHA-Im[2]'), contain negative values.
Some of the files have only few such values (less than 10) but one of them has all but one negative values, see the plot below. Column no. 4 ('ALPHA_o-Im[4]', non-interacting picture) contains some but few negative values as well.
Comment: the column number present in labels of the plot corresponds to Python indexing starting with 0, hence shifted by '-1' meaning the column with 'ALPHA-Im[2]' is plotted.
The fact that it is negative is a sign of something very fishy going on.
The question is what did we do in a wrong way?
The details of our calculations are in the Yambo run file attached, the most significant parameters are:
Qdirection = 0 0 1
QShiftOrder = "less than 3"
Also, we are not quite sure what is the exact meaning of value of 'QShiftOrder'.
Does the integer value relate to the Nth BZ, coefficients of linear combination of base Q-vectors or something else completely?
2) Insignificant 'LongDrXd' effects:
We did not find significant, if any, dependence on changing (direction of) intensity the electric field, paremeter 'LongDrXd' from (1, 0, 0) to (0, 0, 1).
See the below plot comparing fairly equivalent q-points, i.e. "q31" in the case of out-of-plane (perpendicular) LongDrXd on a grid 46x46x18 (with the input file attached) and "q7" for an in-plane LongDrXd on a grid 90x90x1. First, we believed that it might be due to single q-point (calculations not presented here) in the z-direction but this occurs also in the case of multiple q_z coordinates (namely the 46x46x18).
According to the variables explained
https://www.yambo-code.eu/wiki/index.ph ... s#LongDrXd
one should take LongDrXd lie in-plane/axis of the system if a non-3D material is considered.
On the other hand, according to the following tutorial,
https://www.yambo-code.eu/wiki/index.ph ... _direction,
changing the direction to out-of-plane seems to be a common practice.
We expect the polarisation to play more significant role.
Kind regards,
Martin and Ales
we have calculated alpha (which should represent EELS) for a monolayer graphene.
We intend to calculate at q-points outside of the 1st BZ (Brillouin zone) and also separately calculate both q-parallel (in-plane) and q-perpendicular incidence.
We experimented with increasing number of q-points with different q_z coordinates (real-space z-axis is perpendicular to the graphene sheet).
1) Negative alpha outside of the 1st BZ:
Strangely enough, our results with interaction (local field effects), column 2 ('ALPHA-Im[2]'), contain negative values.
Some of the files have only few such values (less than 10) but one of them has all but one negative values, see the plot below. Column no. 4 ('ALPHA_o-Im[4]', non-interacting picture) contains some but few negative values as well.
Comment: the column number present in labels of the plot corresponds to Python indexing starting with 0, hence shifted by '-1' meaning the column with 'ALPHA-Im[2]' is plotted.
The fact that it is negative is a sign of something very fishy going on.
The question is what did we do in a wrong way?
The details of our calculations are in the Yambo run file attached, the most significant parameters are:
Qdirection = 0 0 1
QShiftOrder = "less than 3"
Also, we are not quite sure what is the exact meaning of value of 'QShiftOrder'.
Does the integer value relate to the Nth BZ, coefficients of linear combination of base Q-vectors or something else completely?
2) Insignificant 'LongDrXd' effects:
We did not find significant, if any, dependence on changing (direction of) intensity the electric field, paremeter 'LongDrXd' from (1, 0, 0) to (0, 0, 1).
See the below plot comparing fairly equivalent q-points, i.e. "q31" in the case of out-of-plane (perpendicular) LongDrXd on a grid 46x46x18 (with the input file attached) and "q7" for an in-plane LongDrXd on a grid 90x90x1. First, we believed that it might be due to single q-point (calculations not presented here) in the z-direction but this occurs also in the case of multiple q_z coordinates (namely the 46x46x18).
According to the variables explained
https://www.yambo-code.eu/wiki/index.ph ... s#LongDrXd
one should take LongDrXd lie in-plane/axis of the system if a non-3D material is considered.
On the other hand, according to the following tutorial,
https://www.yambo-code.eu/wiki/index.ph ... _direction,
changing the direction to out-of-plane seems to be a common practice.
We expect the polarisation to play more significant role.
Kind regards,
Martin and Ales