[ase-users] Preconditioned LBFGS - RuntimeError: a1 too small, giving up

[Noam Bernstein]

> On May 18, 2017, at 10:02 AM, Ulrik Leffers via ase-users <ase-users at listserv.fysik.dtu.dk> wrote:
> 
> Hi, 
> 
> I've run into some issues when running the preconditioned LBFGS optimisation on a YLaS3 structure with 20 atoms in its unit cell. It runs about 100 iterations before giving the error, "RuntimeError: a1 too small, giving up". However, it only actually seems to do anything within the first 75 iterations; I tried to plot the energy of the system and the positions of the atoms in the gui, everything is constant from this point. I have attached the script as well as the slurm output and the trajectory file from the optimisation. Any help as to how this error can be avoided would be much appreciated.

The most common cause of such behavior is forces and energies that are not self consistent, typically because of inadequate convergence w.r.t. some parameter or another (SCF tolerance, cutoff can also be an issue for codes that aren’t exactly translationally invariant).  We’d at least need to know what calculator you’re using to be able to say anything more specific.

								Noam


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|U.S. NAVAL|
|_RESEARCH_|
LABORATORY
Noam Bernstein, Ph.D.
Center for Materials Physics and Technology
U.S. Naval Research Laboratory
T +1 202 404 8628  F +1 202 404 7546
https://www.nrl.navy.mil <https://www.nrl.navy.mil/>
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