Molecular systems, theoretical background

Infinite-order sudden approximation (IOSA), electron nuclear dynamics (END), molecular systems, 345-349 Initial relaxation direction (IRD), direct molecular dynamics, theoretical background, 359-361 Inorganic compounds, loop construction, photochemical reactions, 481-482 In-phase states ... 

Wigner rotation/adiabatic-to-diabatic transformation matrices, 92 Electronic structure theory, electron nuclear dynamics (END) structure and properties, 326-327 theoretical background, 324-325 time-dependent variational principle (TDVP), general nuclear dynamics, 334-337 Electronic wave function, permutational symmetry, 680-682 Electron nuclear dynamics (END) degenerate states chemistry, xii-xiii direct molecular dynamics, structure and properties, 327 molecular systems, 337-351 final-state analysis, 342-349 intramolecular electron transfer,... 

Jahn-Teller effect (Continued) theoretical background, 41-44 topological spin insertion, 70-73 two-state molecular system, 58-59 permutational symmetry ... 

Longuet-Higgins phase-based treatment, three-particle reactive system, 157-168 theoretical background, 43-44 observability, 208 quantum theory, 200 Phase-inverting reactions molecular model, 496-499 phase-change rule, pericyclic reactions, 449-450... 

In this chapter, we briefly discuss the theoretical background of polarized x-ray absorption spectroscopy (PXAS). Many of the recent applications of synchrotron radiation to polarized absorption edge structure and to EXAFS are discussed, with particular emphasis being given to the study of discrete molecular systems. We present here some indication of the potential applications of PXAS to systems of chemical and biological interest. 

The various methods used in quantum chemistry make it possible to compute equilibrium intermolecular distances, to describe intermolecular forces and chemical reactions too. The usual way to calculate these properties is based on the independent particle model this is the Hartree-Fock method. The expansion of one-electron wave-functions (molecular orbitals) in practice requires technical work on computers. It was believed for years and years that ab initio computations will become a routine task even for large molecules. In spite of the enormous increase and development in computer technique, however, this expectation has not been fulfilled. The treatment of large, extended molecular systems still needs special theoretical background. In other words, some approximations should be used in the methods which describe the properties of molecules of large size and/or interacting systems. The further approximations are to be chosen carefully this caution is especially important when going beyond the HF level. The inclusion of the electron correlation in the calculations in a convenient way is still one of the most significant tasks of quantum chemistry. 

Before presenting the applications, the theoretical background for the density matrix method should be constructed in molecular terms. For this purpose, a detailed definition of the density matrix of the system should be discussed. Let us consider a molecule at position Ry interacting with an applied laser field of bandwidth 8co and corresponding wave-vector width 8k — 8co/c. Now, it is assumed that the laser beam spot is similar to 8k and a system has only two states described by n> and m ) with respective energies hcontt and ha, within 8co. In this case, the dynamics of the system can be described as... 

In previous chapters, detailed theoretical principles of CT processes in general and photoinduced CT processes in particular have been provided. The next step is the practical application of these principles to systems which will be discussed within the scope of this thesis, namely organic -conjugated donor-acceptor supramo-lecular assemblies. Furthermore, we will draw our attention to CT processes, which are triggered by photochemical stimuli. They provide the theoretical background, which is required to understand the charge-transport properties of wire-type molecular bridges. 

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