原子核量子动能和动量分布的有效第一性原理计算
Efficient first-principles calculation of the quantum kinetic energy and momentum distribution of nuclei
摘要：
在室温及以下的轻核表现出明显偏离经典统计力学预测的动能。这种量子动能导致了从化学到气候学等领域的广泛的同位素效应。它还消除了核动量分布的二阶矩，其中包含有关化学环境的微妙信息，最近已成为深非弹性中子散射实验。在这里，我们将展示如何通过将虚时间路径积分动力学与精心设计的广义朗之万方程相结合，可以大大减少计算量子动能的费用。我们还介绍了一个瞬态各向异性高斯近似的核动量分布，可以计算与忽略不计的额外努力。作为一个例子，我们评估的结构特性，量子动能，和核动量分布的第一性原理模拟液态水。
英文摘要：
Light nuclei at room temperature and below exhibit a kinetic energy which significantly deviates from the predictions of classical statistical mechanics. This quantum kinetic energy is responsible for a wide variety of isotope effects of interest in fields ranging from chemistry to climatology. It also furnishes the second moment of the nuclear momentum distribution, which contains subtle information about the chemical environment and has recently become accessible to deep inelastic neutron scattering experiments. Here we show how, by combining imaginary time path integral dynamics with a carefully designed generalized Langevin equation, it is possible to dramatically reduce the expense of computing the quantum kinetic energy. We also introduce a transient anisotropic Gaussian approximation to the nuclear momentum distribution which can be calculated with negligible additional effort. As an example, we evaluate the structural properties, the quantum kinetic energy, and the nuclear momentum distribution for a first-principles simulation of liquid water.
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