Study of simulation method of time evolution of atomic and molecular systems by quantum electrodynamics
Study of simulation method of time evolution of atomic and molecular systems by quantum electrodynamics
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量子电动力学模拟原子分子系统时间演化方法研究
DOI：
10.1002/qua.24726
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发表时间：
2014
影响因子：
2.2
通讯作者：
A. Tachibana
中科院分区：
文献类型：
--
作者：
K. Ichikawa;M. Fukuda;A. Tachibana
讨论了一种基于量子电动力学的跟踪原子和分子系统时间演化的方法。我们的策略包括通过局域波包来扩展电子场算符，以定义创造算符和湮灭算符，并使用场算符在海森堡图像中的运动方程来跟踪时间演化。我们首先推导出激发算符的时间演化方程，它是两个产生或湮灭算符的乘积，这是构造物理量算符(如电子电荷密度算符)所必需的。然后，我们描述了我们的近似方法来获得电子密度矩阵的时间微分方程，它被定义为激发算符的期望值。通过数值求解方程，我们发现在氢原子和分子的电荷密度中出现了“电子-正电子振荡”，这是由虚拟电子-正电子对的产生和湮灭引起的涨落。我们还发现，考虑电子发射一个光子然后再吸收它的自能过程，电子-正电子振荡的周期变得更短，这可以解释为由于自能而增加的电子质量。©2014 Wiley期刊，Inc.
We discuss a method to follow step‐by‐step time evolution of atomic and molecular systems based on quantum electrodynamics. Our strategy includes expanding the electron field operator by localized wavepackets to define creation and annihilation operators and following the time evolution using the equations of motion of the field operator in the Heisenberg picture. We first derive a time evolution equation for the excitation operator, the product of two creation or annihilation operators, which is necessary for constructing operators of physical quantities such as the electronic charge density operator. We, then, describe our approximation methods to obtain time differential equations of the electronic density matrix, which is defined as the expectation value of the excitation operator. By solving the equations numerically, we show “electron‐positron oscillations,” the fluctuations originated from virtual electron‐positron pair creations and annihilations, appear in the charge density of a hydrogen atom and molecule. We also show that the period of the electron‐positron oscillations becomes shorter by including the self‐energy process, in which the electron emits a photon and then absorbs it again, and it can be interpreted as the increase in the electron mass due to the self‐energy. © 2014 Wiley Periodicals, Inc.