OptaDOS photoemission module

[victorchanglee]

Dear all,

This includes a new module for simulating photoemission in OptaDOS.

Details of the implementation are included in documents/photoemission

A .cell .param and .odi example files are also included in examples/Photoemission

Please, let me know about any issue or question about how to use the module.

Kind regards, Victor

[ajm143]

@victorchanglee I'm confused by a ddome_bin file? What does it contain, and where does it come from? An ome_bin is the optical matrix elements. A dome_bin is the diagonal optical matrix elements, so what does ddome mean? And is that a consistent naming scheme?

[Rebecca-Nicholls]

@victorchanglee Hi Victor - thank you for all of this! I'm in the middle of teaching at the moment but should be able to look at it in ~three weeks time. Andrew has sent you some comments in the meantime. Best wishes, Rebecca

[victorchanglee]

@victorchanglee I'm confused by a ddome_bin file? What does it contain, and where does it come from? An ome_bin is the optical matrix elements. A dome_bin is the diagonal optical matrix elements, so what does ddome mean? And is that a consistent naming scheme?

@ajm143 It contains the second order kp perturbation, which is the band curvature/effective mass. This is currently under "testing"

It is related to how the parallel momentum in ARPES is interpreted. In ARPES, the angle is determined by the parallel momentum of the electrons inside of a crystal. It is usually assign to the crystal momentum or wavevector k. However, the nature of the Bloch theorem makes k only preserved for a defined unit cell or in other words, if we define a supercell, the bands will be folded and thus changing the interpretation of k.

Related to this issue, several band unfolding schemes has being developed (for example, CASTEP has a band unfolding tool), however, in my thesis I took a different look at this momentum interpretation of the band structure.

I used two different approaches, the first one is applying the momentum operator to get the momentum expectation value, which is in fact, the kp first order perturbation already computed in CASTEP in .dome

The second approach I used is a semi-classical momentum, for which I used the band gradient to obtain the electron velocity and the band curvature to get the effective mass. The band curvature is computed as the second order perturbation in the kp method, for which Phil Hasnip and Peter Byrnes provided me with a piece a code to modify Castep.

There is a key word "momentum" that switch between one momentum interpretation or the other. It is under testing since both three approaches gives different answers.

[ajm143]

@pjh503 This is technically a CASTEP issue. But seems to fit better with this PR.

We seem now to have a ddome filename. I think that name could be confusing.

• ome are the optical matrix elements j,i
• dome is the diagonal optical matrix elements I=j. Hence d stands for diagonal
• ddome second order k.p perturbation, I=j. Hence the first d stands for derivative, and the second d for diagonal.

I'm worried that this might get messy if we use d to mean two different things. What are your thoughts?

[pjh503]

I agree that ddome_bin would be confusing, the question is what it should be called. I prefer "d" to mean "derivative", but unfortunately we've already used it for "diagonal".

I would also prefer the name to reflect the fact that it is a derivative with respect to "dk", as we can imagine cases whether we look at the derivative with respect to other things (e.g. strain, phonon mode).

[ajm143]

.dome_dk ? I agree we're using d to mean two different things here... maybe we get away from omes and call it de_dk or similar? .bands_dk ?