Molecular dynamics electron-exchange reactions

In this article, particular attention has been paid to the results of laboratory experiments that have provided information about the molecular dynamics of electronically adiabatic atom-exchange reactions. For a reaction like A + BC - AB + C, where the possibility of crossing between different electronic states can safely be ignored, a theoretical study comprises three distinct stages [20] (a) the determination of the potential-energy hypersurface, (b) the solution of the equations that describe the motion of A, B, and C under the influence of V, and (c) the averaging of the results of these trajectory calculations so that they reflect the distribution of collisional... 

Quantum-mechanical ab initio calculations for small molecular systems are widely used these days as an instrument in studying problems in various Helds of chemistry and molecular physics . Most studies deal with ground-state phenomena, i.e. the structure and properties of compounds, thermal reaction pathways and dynamical behavior based on this information. There has been a noticeable increase in excited-state studies in recent years, however, in particular in connection with problems in molecular spectroscopy, in ionization processes or in the detailed study of photochemical reactions, such as photodissociation, energy-transfer and charge-exchange reactions. The calculations are especially powerful for small molecules (for example, for systems up to SO electrons and six atoms other than hydrogen), and hence numerous applications are found in particular in the area of atmospheric and interstellar chemistry and in the study of combustion processes. In these Helds it is often found that experimental and theoretical studies are undertaken in close conjunction and that the two yield complementary data which, taken together, are able to clarify a process. In other instances it is not uncommon that for short-lived species the values obtained from calculations are so far the only ones available. 

In this chapter we focus on methodological and computational aspects that are key to accurately modeling the spectroscopic and thermodynamic properties of molecular systems containing actinides within the density functional theory (DFT) framework. Our focus is on properties that require either an accurate relativistic all-electron description or an accurate description of the dynamical behavior of actinide species in an environment at finite temperature, or both. The implementation of the methods and the calculations discussed in this chapter were carried out with the NWChem software suite [1]. In the first two sections we discuss two methods that account for relativistic effects, the ZORA and the X2C Hamiltonian. Section 12.2.1 discusses the implementation of the approximate relativistic ZORA Hamiltonian and its extension to magnetic properties. Section 12.3 focuses on the exact X2C Hamiltonian and the application of this methodology to obtain accurate molecular properties. In Section 12.4 we examine the role of a dynamical environment at finite temperature as well as the presence of other ions on the thermodynamics of hydrolysis and exchange reaction mechanisms. Finally, Section 12.5 discusses the modeling of XAS... 

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