Quantum Mechanics and Electronic Structure

Irmgard Frank

Quantum mechanics is perceived as a theory that is difficult to understand with strange philosophical consequences. This is due to the Copenhagen interpretation of quantum mechanics. On the basis of the knowledge accumulated in modern computer simulations of many-particle problems, a different approach is presented that is purely deterministic. To arrive at this simpler picture, it is sufficient to treat nuclear motion classically. It is argued that this is justified by the different nature of nuclear motion compared to electronic structure, which must be described quantum-mechanically. The underlying approximation leads directly to the theory that is mainly used nowadays to simulate chemical reactions. As a result, electronic structure develops with time without any wavefunction collapse.

Fanica Cimpoesu, Mihai V. Putz, Marilena Ferbinţeanu

Robin Findlay Hendry

Jaime Keller

Quantum Mechanics is a successful model to describe physical phenomena. We show that a simple set of postulates about the description of objects in Nature allows the derivation of the principles of QM, transforming this theory into a deductive approach to Physics. The main postulate is: Objects are described as energy distributions in Space–Time. 1 Quantum Mechanics from START It is universally accepted that Quantum Mechanics is a successful model to describe physical phenomena, in particular of the electronic structure of atoms, molecules and solids. As such it has been reformulated in several different forms (see for example: Nine formulations of quantum mechanics, Daniel F. Styer et al. [15]). The aim of the present paper is to show that a simple set of postulates about the description of objects in Nature allows the derivation of the principles of QM, transforming this theory into a deductive approach to Physics. In our approach the main postulate is: Objects are described as energy distributions in Space–Time. The theory is in fact a systematic mathematical analysis of this postulate and of other general considerations about action, energy–momentum and the role of the theory as a useful description of Nature. The paper also shows the fundamental and basic status of Density Functional Theory, also contained in our approach. The initial mathematical structure is a geometric (quadratic form based) union of space, time and action. In physics bundles of trajectories are used to describe the objects of nature: distribution of heights over a surface, a real object is described as a bundle of space-time trajectories, here we use a description as a bundle of action valves in space-time (energy densities in space following light-like lines). The author is fully aware that the presentation is strongly guided by the knowledge of the usual computational approach to study atoms, molecules and condensed matter electronic structure.

Walter A. Harrison

The basic approach: foundations simple cases Hamiltonian mechanics. Electronic structure: atoms molecules crystals. Time dependence: transitions tunnelling transition rates. Statistical physics: statistical mechanics transport theory noise. Electrons and phonons: energy bands electron dynamics lattice vibrations. Quantum optics: operators phonons photons coherent states. Many-body effects: coulomb effects co-operative phenomena magnetism shake-off excitations.

James E. House