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Building a potencial energy surface for the ground singlet state of the hydrogen peroxide
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Resumo(s)
The hydrogen peroxide system has attracted widespread attention due to its overwhelming
importance in many chemical processes such as combustion, atmospheric and interstellar
chemistry.
The main goal of the present PhD thesis is the construction of a six-dimensional
Potential Energy Surface (PES) for the ground state of the H2O2 system with chemical
accuracy in order to achieve trustworthy kinetic data. The analytical representation of
the PES is based on a double many-body expansion (DMBE) formalism, where a 3 3
matrix is used to accurately reproduce all the dissociation channels.
The rst part of this thesis concerns the concept of PES, the coordinates used to represent
it as well as its major topological features. A survey of the theoretical framework of
the ab initio calculations and the general strategy to obtain the analytical representation
of the PES are also reported. The second part focuses on the description of the ab initio
electronic calculations performed for mapping the most important regions of the con guration
space. An extrapolation/scaling scheme is proposed to accomplish high-quality
ab initio energies. The parameters used in this procedure are obtained by interpolation
among several reference geometries.
This new DMBE hydrogen peroxide PES also accounts for the electrostatic dipoledipole
interaction between two OH(2 ) fragments. The functional form used to represent
the short-range interactions is based on a sum of polynomial functions of the fourth degree
multiplied by a range factor, both built with intrinsic permutation symmetry and centred
at speci c reference geometries, to which the ab initio points computed are assigned based
on a k-means algorithm.
Finally, important features of the model function are characterized and the major
conclusions are summarized. Further improvements and possible applications for the
present potential are also outlined.
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Química teórica Superfície de energia potencial Peróxido de hidrogénio Cálculos ab initio de estrutura eletrónica