how to pass the fine tune lenths test to obtain a two-probe-system?

[fanjiaping]

Dear Friend,

  Recently, I build up two two-probe-systems. One(sixsixcenterauau.py,the length of eletrode I set is 4.078 ang) of them could pass the fine tunes lengths test to offer a structure, while the other(two.py) could not pass the test even after shortening the length of the electrode(always report the length of center region is too small). I have three questions as follow. 1. How can I fabricate the center region to pass the fine tunes lengths test? 2. If the structure is not obtained via the fine tunes lengths test (unselected), the calculation result is justice or not? 3. What kind of systems could pass the fine tunes lengths test, in other words, which parameters should the as-constructed structure be of to pass the test? Thank you ahead for your response.

Best regards!

[Anders Blom]

Try with at 3 (or more) gold layers on both sides. It's the left electrode which is problematic.

[fanjiaping]

you mean the left gold lays of center region are not enough?but why the first two-probe-system(sixsixcenterauau.py) can pass the fine tune lengths test although it is the same in the center region as the two.py?

[fanjiaping]

 thank you ! I have solved the problem by adding a golden layer to the center region, meanwhile keeping each electrode as two layers .is it reasonable?

[Anders Blom]

The trick to getting it to work, is to give the tool enough information to work with. It needs to find a clear repetition pattern so assign as "electrode". Therefore, adding a few layers make it work.

However, you should at least double the electrode, which fortunately is extremely easy (just enter 2 for electrode repetition), or your system will either not converge or show artifacts. The electrode is too short, which will certainly introduce non-physical scattering.