Institute for Modeling and Innovative Technology, IMIT (CONICET-UNNE), Argentina.
Phys Chem Chem Phys. 2014 Mar 14;16(10):4420-38. doi: 10.1039/c3cp52685b.
The search for a QED-based (and then QFT-based) formalism that brings solid grounds to the whole area of relativistic quantum chemistry was just implicit in the first decades of the quantum theory. During the last few years it was shown that it is still unclear how to derive a well-defined N-electron relativistic Hamiltonian, and also the way negative-energy states may contribute to electron correlation. Furthermore, the relationship among electron correlation and radiative QED corrections is even more difficult to guess. These are few of the fundamental problems that need to be solved before such a program of research is finished within the wavefunction approach to quantum physics. The polarization propagator formalism was developed as an alternative approach to study atomic and molecular properties within both regimes, relativistic and nonrelativistic. In this article we expose how far away one can go today working with polarization propagators, until including QED (and afterwards QFT) effects. We will uncover its deepest formal origin, the path integral formalism, which explains why polarization propagators can be written formally the same in both regimes. This will also explain why the NR limit is obtained scaling the velocity of light to infinity. We shall introduce a few basic aspects of elementary propagators to show what they have in common with polarization propagators. Then we shall remark on the most important news that appears with the latter ones. Within the relativistic regime the contributions of negative energy orbitals to electron correlation are straightforwardly included. New insights on the relationship between spin and time-reversal operators are also given, together with an ansatz on how to consider both, QED and electron correlation effects on the same grounds. We focus here on the treatment of NMR spectroscopic parameters within such a formalism, that is still not broadly used by the quantum chemistry community. Most of the other response properties can be treated in a similar manner.
寻找一种基于 QED（然后是 QFT）的形式体系，为相对论量子化学的整个领域提供坚实的基础，这在量子理论的最初几十年中只是隐含的。在过去的几年中，已经表明，如何推导出定义明确的相对论 N 电子哈密顿量，以及负能态如何可能有助于电子相关，仍然不清楚。此外，电子相关与辐射 QED 修正之间的关系更难猜测。这些是在波函数方法完成相对论量子物理研究计划之前需要解决的几个基本问题。极化传播子形式体系作为一种替代方法被开发出来，用于研究原子和分子在相对论和非相对论两种情况下的性质。在本文中，我们将展示在今天使用极化传播子的情况下可以走多远，直到包括 QED（以及随后的 QFT）效应。我们将揭示其最深层次的形式起源，即路径积分形式体系，该形式体系解释了为什么极化传播子在两种情况下都可以形式上相同地书写。这也将解释为什么在将光速缩放为无穷大时可以得到 NR 极限。我们将介绍一些基本的基本传播子方面，以展示它们与极化传播子有何共同之处。然后，我们将指出后者出现的最重要的消息。在相对论范围内，负能轨道对电子相关的贡献是直接包含的。还给出了自旋和时间反演算子之间关系的新见解，并提出了一个假设，即如何在相同的基础上同时考虑 QED 和电子相关效应。我们在这里关注这种形式体系处理 NMR 光谱参数的方法，这种方法在量子化学界还没有广泛使用。大多数其他响应特性可以以类似的方式处理。
