Dear phylyh,

I might be able to help you because I'd studied almost the same system as you with ATK.

(please see "fig.pdf", I feel it's miracle!)

When I tried the calculation for such a system, I encounterd the same trouble as you.

Judging from a conclusion, the solution is not to use "DobuleZeta" or "DobuleZetaPolarized" basis.

I don't know why, but when I used DZ or DZP in this system, SCF convergence got suddenly worse.

On the other hand, when I used SZP for both "C" and "Fe", the calculation was normally completed

(Parhaps SZ for both "C" and "Fe" is also good).

In addition, "Initial scaled spin" you designate is not good because (5,5)CNT is not spin-polarized.

("Initial scaled spin" is relevant to SCF convegence in some cases)

It seems natural that "Initial scaled spin" for Fe is 1 and "Initial scaled spin" for C is 0.

I attach the modified version of script(input2.py).

I only changed the "Initial scaled spin" for both central region and electrode in "input2.py".

I recommend the further modifications as follows:

1. k-point sampling for C-direction: from 500 to 100,

2. basis set for Fe: from DZP to SZP or SZ,

3. initial_density_type: from InitialDensityType.NeutralAtom to InitialDensityType.EquivalentBulk,

and if you're interested in finite-bias calculation,

4. electrode_constraint: from electrodeConstraints.Off to electrodeConstraints.RealSpaceDensity or electrodeConstraints.DensityMatrix.

I hope your calculations are done well!