  We present a simple protocol which allows fully automated discovery of
elementary chemical reaction steps using in cooperation single- and
double-ended transition-state optimization algorithms - the freezing string and
Berny optimization methods, respectively. To demonstrate the utility of the
proposed approach, the reactivity of several systems of combustion and
atmospheric chemistry importance is investigated. The proposed algorithm
allowed us to detect without any human intervention not only "known" reaction
pathways, manually detected in the previous studies, but also new, previously
"unknown", reaction pathways which involve significant atom rearrangements. We
believe that applying such a systematic approach to elementary reaction path
finding will greatly accelerate the possibility of discovery of new chemistry
and will lead to more accurate computer simulations of various chemical
processes.
