Dynamic QM/MM: A Hybrid Approach to Simulating Gas–Liquid Interactions - Multiscale Molecular Methods in Applied Chemistry - page 63

Fig. 9 Distribution of the final translational energy (in eV) of OH for each angle of incidence
( y ¼ 0 ,30 ,45 , and 60 ) i

here, are HNO 2 and HNO 3 , both of which have smaller and much narrower distribu-
tions of translational energies and are largely independent of incidence angle. It is
thought that this is because the reactive channels that govern these products involve
a proton transfer event, and are not dependent directly upon a primary collision
event.

5 Summary

In this chapter we reviewed the details of our theoretical methods that are used to
describe gaseous atoms scattering from liquid surfaces. Scattering experiments of
this type allow for the direct study of the surface reactivity of liquids, including
studies of the partitioning of molecular energy transfer into various vibrational,
rotational, and translational modes of the scattered products. One of the complex-
ities in modeling such a dynamic system at hyperthermal energies is that many
chemical changes can occur (i.e., the making/breaking of several bonds), and a
priori knowledge of when and where this will occur is not easy to estimate in the
absence of a simulation. Additionally, the spatial length scale needed to describe
gas-surface reactions is larger than what can normally be computed purely with ab
initio QM. Thus we use a hybrid approach that partitions the system into reactive
and nonreactive regions to be treated by a dynamics QM/MM approach.
The nonreactive regions (thousands of atoms) were described with predeter-
mined force fields (OPLS-AA) using MM, and the reactive regions (hundreds of