[DFTB-Plus-User] MD runs terminate without warning

[Vanessa Gruner]

Greetings,

I'm attempting to perform DFTB-MD to simulate the bombardment of a quartz
surface by an atom using dftb+ 1.2.2. My simulations have exhibited some
strange behaviour. When I run my input (see attached), which consists of a
small alpha-quartz substrate and an impinging atom, the simulation ends
(almost always) without giving any error before the MD simulation finishes.
Some simulations progress much farther than others, but usually the
simulations terminate around 10 time steps- sometimes before and sometimes
much later (well after the impinging atom contacts the substrate). Also, I
notice that if you run identical input again, the simulation terminates at
a time step from a previous run. I've tried replacing the
"DivideAndConquer" option for the "Eigensolver" with "RelativelyRobust",
but that didn't really change the outcome.

I observed that simulations of the same quartz configuration in the absence
of a bombarding ion end normally (i.e., after the number of time steps
specified in the input). So, it would appear that the configuration of the
substrate is not causing problems, but rather the atom that is moving
toward the substrate. Is there something in my input that is inappropriate
for these types of simulations? Also, I'm curious about the fact that
identical input does not result in the identical output (i.e., failure at
the same time step and # of iSCC). The velocities for each atom are
specified in the input, so these don't vary between runs. I'm assuming that
the initial forces between atoms, which are not specified in the input, are
changing between runs and that results in the differences in output. Is
that correct?


Thanks,
Vanessa

PS I should note that these simulations are run using pbc-0-3/O-O.skf,
 pbc-0-3/Si-O.skf and pbc-0-3/Si-Si.skf.
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