[DFTB-Plus-User] Convergence issues in DFTB+ calculations?

[Bálint Aradi]

Dear Hemanth,

first of all, please check carefully, whether your system is 
physically/chemically meaningful at all (I did not check it).

Otherwise, a common strategy is for large metallic systems to start with 
a very high electronic temperature (e.g. 100000 K), converge it at that 
temperature, then start a new calculation with lower electronic 
temperature but using the converged charges of the previous calc as 
initial guess (via ReadInitialCharges = Yes).

Using this technique, I could get a converged density for your system 
using 100000, 10000, 1000 and 300 K.

A few remarks to your input file:

* You should not use the 3rd order correction with the mio-set. If you 
wish to have 3rd order correction, use the 3ob set instead.

* If you use 3rd order, you should use ThirdOrderFull (and not 
ThirdOrder), as suggested in the manual.

* Your cell is quite large, so I don't think you need any k-points apart 
of Gamma. (Which would make the calculation significantly faster).

Actually, as it turns out, if you make those changes, you system even 
converges without the trick with the high temperatures, directly at 300 K.

Best regards,

Bálint


-- 
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
http://www.bccms.uni-bremen.de/cms/people/b-aradi/


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