convergence problem

[Ambika kumari]

After putting gas molecule in device configuration, does simulation converge?
I put multiple gas molecule in device configuration and running in super computer by using 240 core but from yesterday it has not calculated i-v curve for a single point, it seems nothing is happening.

[AsifShah]

Depending on number of k points & size of device, transport calculations usually take long time.

[Ambika kumari]

total 250 atoms
for test I took k value 1*1*1 still same.

[AsifShah]

Sometimes it doesn't converge because K points are not enough. 1x1x1 could be one problem. Check log file and save it then run with higher k points for same time & compare two log files to see if K point convergence is the issue

[Ambika kumari]

In log file I am getting nothing, it just mention 16 task will be calculated.
Kindly see the attachment

[AsifShah]

I see you are using Gold (as electrode I guess). From my experience with Gold adsorption calculations they taken long to optimize (converge). I normally run from command line & not from user interface & I see two files apart from .py during run. One is log file & another is name something like optimizationxxxxxx.log . Most infiormation of optimization were found in this optimizationxxx.log file.

[Ambika kumari]

Optimization converged.
Now I am calculating I-V curve.  K point is 2*5*60. At 1st point calculation converged in 40 steps, at 2nd point it didnot converged. Please see the attachment. When K point was 2*5*50, then at 1st point calculation conversed in 38 stepst and at 2nd point calculation converged in 95 steps and at 3rd point calculation did not converged.  Attachment is for k=2*5*60 How to currect it
.
Thanks

[AsifShah]

If you are using Semiempirical calculator, then in that go to iteration control & if you have unticked no scf iteration then below it there will be maximum steps written as 100, change it to 400 & recompute. I am not sure but there is a way I guess to recompute only not converged points instead of rerunning whole calculations.

[Ambika kumari]

400 is too high it will take long time.

[AsifShah]

You need to increase it thats the only way. I faced same issue some time ago but got results.
Try 300 maybe

[Ambika kumari]

ok Thanku. I will check.