Dear Christoph, 

Thank you so much for your reply. 

I've had a look at the Kwant tutorial about the discretization. However, the response I am seeing isn't consistent with the idea of an energy limit being reached. 

It appears that as I change the number of lattice points, therefore the grid spacing, the response of the system changes as shown in the attached image. The graphs show the state being evolved in Tkwant with the expectation values of the Pauli spin matrices plotted. 
 
For 20, 40 and 120 lattice points the graphs show an expected and similar response. For 60, 70 and 100 the graphs show no evolving of the state or an unphysical response. It appears to be very inconsistent with the grid spacing value.

Could there be another cause of this result, for example how the system is built rather than a continuum limit?

Thank you for any more help with this. 

Best wishes,
Isobel




From: Christoph Groth
Sent: Thursday, March 16, 2023 15:05
To: Clarke, Isobel
Cc: kwant-discuss@python.org
Subject: Re: [Kwant] How does the grid spacing in kwant.continuum.discretize effect the system?

Hi Isobel,

As you decrease the discretization grid spacing you should approach the
continuum limit.  For example, the band structure should become more and
more accurate also for larger momenta.

Did you check the Kwant tutorial on the discretizer?  In particular the
example comparing a=1.0 and a=0.25:
https://kwant-project.org/doc/1/tutorial/discretize#limitations-of-discretization

Tkwant should not really matter here.  I suggest that you first check
whether your discretization behaves as it should without even using
tkwant, for example by looking at the band structure.

Cheers
Christoph