First-Principles-Based Multiscale, Multiparadigm Molecular Mechanics and Dynamics Methods for Describing Complex Chemical Processes - Multiscale Molecular Methods in Applied Chemistry - page 25

In another application we have examined the Auger decay process in a
diamond nanoparticle and in silicon, relevant to the etching of semiconductor
substrates using low energy electron-enhanced etching processes [ 92 ]. We found,
for the diamond case, that ionizing core electrons induced selective breaking of
bonds via a variety of mechanisms, i.e., through direct excitation and ionization
of valence electrons, or through indirect heating, or even in a small subset of
cases, a billiard-ball like scattering away of valence electrons through ejection
of neighboring bonding electrons (see Fig. 12 ). Our results were consistent with
ion ejection data from photon-simulated desorption experiments performed on
diamond films.
Our current development of eFF involves adding explicit electron exchange-
correlation potentials, core pseudo-potentials, and extended support for systems
with significant p- and d-character. Using eFF, we're now able to study the effect of
highly excited electrons in the dynamics of material subjected to extreme condi-
tions, including those described before, as well as other open problems in interfacial
shock instabilities, radiation damage, to name a few.
As simulation requirements shift to larger length scales and longer times and
system properties are amenable to homogenization in space and averaging in time,
for example in characterizing the conformational behavior of supramolecular
systems, coarse-grain methods tuned from finer scale ones (e.g., QM, MM) repre-
sent a suitable and more efficient alternative for evolving the dynamics of systems
with reduced degrees of freedom. The following section discusses our progress
in developing coarse-grain force fields and time-lower bound solutions to the
resulting rigid multibody EOM.

Fig. 12 Single Auger trajectory after ionization of a carbon core electron at the center of the
diamond nanoparticle ( m elec m p ). Valence electrons surrounding the core hole with the same

spin as the ionized core electron are highlighted in red , green , blue , and purple . Distance of
valence electrons from the core hole, showing the green electron filling the core hole, the red
electron being ejected (and trapped after 20 fs, not shown), and the blue and purple electrons being
excited. From [ 93 ]

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