[DFTB-Plus-User] Question about hessian generation to use in modes
Reinaldo Pis Diez
reinaldo.pisdiez at gmail.com
Tue Feb 8 16:12:22 CET 2011
Dear dftb+/modes users,
I was running the modes utility to get the frequencies of some
aggregates. There is no problem with that utility but I've seen a
non-expected behavior in the prior runs with dftb+ needed to create
the hessian.
Firstly, I run dftb+ with the ConjugateGradient option to the Driver
keyword to optimize the geometry of the isolated aggregate. It took
about 100 cycles to optimize with a MaxForceComponent of 0.01 a.u.,
no too strict but the calculation is part of a set of jobs on
several aggregates with increasing size and convergence becomes
difficult for large sizes.
Secondly, I prepare dftb_in.hsd with the SecondDerivatives option to
Driver to generate hessian.out. I append the geometry that was
optimized in the previous step, using the *.gen file. But, to my
surprise, the job starts with a geometry optimization again before
generating the hessian. It took about 30 cycles now, and the problem
here is that I cannot get the re-optimized geometry as the
OutputPrefix option is not valid in SecondDerivatives.
As a consequence of this the hessian and the optimzed geometry I'm
using for modes do not correspond to the same dftb+ run.
Any hints will be appreciated.
Regards,
Reinaldo
PS: Sorry for the long mail!
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