Quantum electrodynamics, QED

With the exception of recent extensions to electroweak theory [1] chemistry deals exclusively with electromagnetic interactions. The starting point for a quantum theory to describe these interactions is the Lagrangian formalism since it allows the correct identification of conjugated momenta appearing in the Hamiltonian [2]. Full-fledged quantum electrodynamics (QED) is based on a Lagrangian of the form... 

A systematic development of relativistic molecular Hamiltonians and various non-relativistic approximations are presented. Our starting point is the Dirac one-fermion Hamiltonian in the presence of an external electromagnetic field. The problems associated with generalizing Dirac s one-fermion theory smoothly to more than one fermion are discussed. The description of many-fermion systems within the framework of quantum electrodynamics (QED) will lead to Hamiltonians which do not suffer from the problems associated with the direct extension of Dirac s one-fermion theory to many-fermion system. An exhaustive discussion of the recent QED developments in the relevant area is not presented, except for cursory remarks for completeness. The non-relativistic form (NRF) of the many-electron relativistic Hamiltonian is developed as the working Hamiltonian. It is used to extract operators for the observables, which represent the response of a molecule to an external electromagnetic radiation field. In this study, our focus is mainly on the operators which eventually were used to calculate the nuclear magnetic resonance (NMR) chemical shifts and indirect nuclear spin-spin coupling constants. 

The relativistic problem of many electron systems, described by quantum electrodynamics (QED), is nowadays an interesting topic of research. The high complexity of... 

DCB is correct to second order in the fine-structure constant a, and is expected to be highly accurate for all neutral and weakly-ionized atoms [8]. Higher quantum electrodynamic (QED) terms are required for strongly-ionized species these are outside the scope of this chapter. A comprehensive discussion of higher QED effects and other aspects of relativistic atomic physics may be found in the proceedings of the 1988 Santa Barbara program [9]. 

Calculation of electromagnetic properties within the formalism of relativistic quantum electrodynamics (QED). 

Abstract. There is presented a consistent energy approach to the quantum electrodynamics (QED) theory of the discharge of a nucleus with emission of a y radiation and further muon conversion, which initiates this discharge. A numer-... 

In quantum electrodynamics (QED) the potentials asume a more important role in the formulation, as they are related to a phase shift in the wavefunction. This is still an integral effect over the path of interest. This manifests itself in the phase shift of an electron around a closed path enclosing a magnetic field, even though there are no fields (approximately) on the path itself (static conditions). As can be shown the result of such an experiment is gauge-invariant, allowing the use of various choices of the vector potential (all giving the same result). 

In formulating quantum electrodynamics (QED), it has been found convenient to introduce the electromagnetic interaction with charged particles via the potentials instead of the fields. Consider a particle of charge q traveling on some path P from i to 2. Then the magnetic change in phase of the wavefunction is just... 

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