[DFTB-Plus-User] OpenMP with DFTB+

Bálint Aradi aradi at uni-bremen.de
Thu Nov 21 18:09:03 CET 2019

Dear Alessandro,

Most probably, your linked LAPACK / BLAS libraries which are not
threaded. In usual calculations DFTB+ spends over 90% of its runtime in
the diagonalisation routine of the external library. It that is not
threaded, you basically won't see any effects when allowing threads.

Make sure, you link threaded LAPACK and BLAS implementation to the code.

You could also try to use the binary from


as that is linked against a performant and threaded library.

Best regards,


On 21.11.19 14:26, Alessandro LANDI wrote:
> Dear DFTB+ users,
> I have a problem related the use of DFTB+ with OpenMP.
> I am using a Linux Ubuntu 14.04.6, with 8 cores.
> I have tried to run the attached input file (conjugate gradient
> optimization of a rubrene cell with cell axes invariated) both using an
> old DFTB+ version (1.3) and using the latest stable release (19.1), but
> in both cases when typing the "top" command under Linux environment, I
> get a %CPU usage of 100%, thus indicating a single thread in use.
> I have used the attached makefile to compile the DFTB+ code (I attach
> both 1.3 and 19.1 version). I have used gfortran and gcc 7.4.0 versions.
> I have installed blas, lapack, arpack and atlas libraries.
> Moreover, of course I have set "export OMP_NUM_THREADS=8" in my Linux
> environment.
> I have tried to browse the web looking for similar problems, but
> unfortunately, I found nothing. 
> Do you please have any suggestions on what I am doing wrong?
> 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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> DFTB-Plus-User at mailman.zfn.uni-bremen.de
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Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen

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