Espaço do momento: modelos da química quântica / Momentum Space: Quantum Chemistry Models

AUTOR(ES)

Willian Hermoso

DATA DE PUBLICAÇÃO

2008

RESUMO

In a conventional course in Quantum Chemistry, the models usually presented to illustrate the use of some quantum mechanical tools that are relevant for a comprehension of the structure of matter at the atomic and molecular levels are approached in a way that has been termed, in a more formal presentation, as position representation. In this representation, the state of a system is described by a wavefunction that is dependent on the positions of all particles that define the system. As a consequence of this presentation, chemistry students assimilate a distorted conception that in nature the state of a system must necessarily be described in terms of particles positions. Here we show that this is not the only way to approach quantum mechanically the description of a physical system. In an alternative way, known as momentum representation, the state function is expressed in a way that it is explicitly dependent on the momentum of each particle. There are two ways to obtain wavefunctions in the momentum representation. In of them, use is made of a Fourier transform of the wavefunctions in the position representation, and in the other one, an attempt is made to solve Schroedinger´s equation directly in the momentum representation. In this work, we have discussed these two approaches by examining the most common models studied in a Quantum Chemistry course, namely: the particle in a box, the harmonic oscillator, the hydrogen atom, the helium atom, the hydrogen molecular ion, and the hydrogen molecule. We have tried to show a different physical perspective in the description of these systems as well as a distinct mathematical approach than the usual one, and also the difficulties, mainly mathematical, of applying and teaching this representation in a Quantum Chemistry course.

ASSUNTO(S)

quantum chemistry models química quântica espaço de configurações configuration space modelos da química quântica representação do momento momentum representation

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