Regarding Two-probe convergence

[Timbaktoo]

Can someone please take a look into this file and let me know what improvement I can make in the initial-parameters for a better convergence(and probably in shorter time). Right it has been 40 hours and the calculations are still running  

My system: Processor: AMD Athlon(tm) 64 X2 Dual Core 4400+
                 RAM: 3GB

Thankyou.

[Anders Blom]

Please post output too. 40 hours - how many iterations are done within this time? Expect it to take about 70-80 iterations, this is a difficult system!

[Anders Blom]

Parameters seem reasonable, but you are running a geometry optimization, is that what you really wanted?

Always try to converge the single point calculation (no optimization) first, to ensure that you have the right parameters for the quantum-chemical model. Then you can start relaxations, if necessary.

Note that each step in the optimization easily may take 10-12 hours, esp. if you run on a laptop or so. Multiply this by 10-20 steps of convergence for the geometry optimization, and you get quite a long time. That's why a system like this, esp. with so high k-point sampling (10x10) should be run on a cluster, in which case (precisely thanks to the k-points sampling in particular) will scale very nicely and perhaps run 10-20 times faster on, say, 16-32 nodes.

[Timbaktoo]

Thanks Anders.
The calculations are still running, so no output file. I tried attaching the .nc file that has still not converged. But it exceeds the allowed attachment limit of 512KB as it popped-up. The count is 35 iterations (it is running at the rate of approx. 4 iterations per hour!!).

The dRho is still fluctuating from E-1 to E-3 from 20th iteration upto 35th. and same goes for the dEtot values. Do you think these are not converging?? I guess so.

I think I would switch over to a cluster. One quick question, since the cluster that I have access to is Linux base, so will this work if I prepare the script file on VNL and run that .py file on ATK? Just to save myself from scripting???

Thankyou.

[Anders Blom]

Right, 4 iterations per hour, that's quite normal for a Windows laptop. It will be MUCH faster on the cluster.

It might very well be converging. This is one of the most difficult systems around, and 70-80 iterations are typically needed (and that's the best we ever got this system to do, sometimes it needs 200...!).

Sure, the scripts are fully cross-platform compatible, so you can prepare the script in VNL on Windows, save it, run it on the cluster, and then reimport the VNL file back to Windows VNL and view the results. You can even bring over the NC file and do the second step analysis (transmission etc) on Windows, although you will probably want to run that on the cluster too, as it scales even better with the number of nodes.

[Timbaktoo]

Thanks Anders.
Yeah, in previous calculations it went upto 140 iterations and days to converge.

I stopped this previous simulation as I felt it is going nowhere. Will run it on the cluster then to see if it converges quickly.