We should also note that a 1D system like this might not be the best one for testing the voltage drop, since the 1D chain screens the potential very poorly. I also think, when looking more closely at it, that the XY unit cell should be expanded in this example; there seems to be some interaction with the repeated chains in these directions. I would also sharpen the tolerance, not sure how much it helps, but the default 1e-5 is a bit on the liberal side for certain quantities (probably not current, but maybe more "intrinsic" quantities.
I would also like to point you to
the beautiful voltage drop pictures posted by "nori", that really show that ATK can compute this accurately and "correct", if the system is correspondingly set up.
The 1D Li-H2-Li should in general not be seen a very suitable two-probe test system; many of its properties are quite artificial, in fact. Its primary appeal is that it's fast to compute, and so it serves as a good example to teach people
how to compute various things, but it's less suitable for
analyzing the results!
Finally, if you are interested in computing the voltage drop, you might find
my new post on extracting the effective potential from a VNL file useful!
