[DFTB-Plus-User] Problem with geometry convergence

Alessandro LANDI alelandi1 at unisa.it
Fri Dec 20 10:41:17 CET 2019


Dear DFTB+ users,
I am trying to optimize the molecules in the unit cell of C10-DNBDT (see
gen and cif files attached) without changing the lattice constants. I am
using DFTB+ 18.2, the Conjugate Gradient method and Supercell Folding
k-points.
Unfortunately, I did not manage to reach convergence, as the Maximal force
component oscillates between 10^-3 and 10^-2, even after several (more than
1000) Geometry steps.

Since in the past I have managed to optimize several organic molecules
(rubrene, pentacene, DNTT, etc,) I honestly do not understand what I am
doing wrong.
Following some threads I have found online, I have also tried to change the
number of k-points (2, 1 and 6 instead of 4) but I still got the same
problem: the Maximal force component oscillates between 10^-3 and 10^-2.

Could you please give me any suggestions on what I should do in order to
reach geometry convergence?


Thank you in advance.

Best regards,
Alessandro


-- 
Alessandro Landi, Assegnista di Ricerca
Dipartimento di Chimica e Biologia "Adolfo Zambelli"
Università degli Studi di Salerno
Via Giovanni Paolo II, 132 - 84084 - Fisciano (SA)
Phone number 089969390
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