从第一性原理确定氮的基本性质。III. 分子极化率和磁化率的温度和频率依赖性
Determination of fundamental properties of nitrogen from first principles. III. Temperature and frequency dependence of the molecular polarizability and magnetic susceptibility
- University of Warsaw, Faculty of Chemistry（华沙大学化学系）
- European Centre for Theoretical Studies in Nuclear Physics and Related Areas (FBK-ECT*)（核物理及相关领域欧洲理论研究中心）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
该研究为氮分子极化率和磁化率温度及频率依赖性做第一性原理计算，用多种方法确定其温度依赖性，理论极化率与测量相符但精度低，主要用于结合实验生成半经验估计，还报告了磁化率理论值并解决与实验数据的差异。
AI中文摘要：
本文是关于计量学中氮性质理论确定系列论文的第三部分。我们给出了氮分子（N₂）分子极化率和磁化率温度及频率依赖性的第一性原理计算。利用结合多种电子结构方法的稳健复合方案，计算了一系列核间距下静态极化率、柯西系数（直至六阶）和各向同性磁化率的纯电子贡献。通过振转平均和路径积分蒙特卡罗（PIMC）两种独立方法确定了50 K至2000 K的温度依赖性。理论得到的极化率与高精度测温测量结果相符，但精度较低。理论数据主要用于与现有实验结果结合，生成迄今未测量的各种量的半经验估计。例如，我们确定了关键参考温度下静态极化率的高精度半经验估计值。此外，我们报告了磁化率的理论值，强调了顺磁贡献的重要性，并解决了该量与实验数据的显著差异。
英文摘要：
This work is the third part of the series of papers that focus on the theoretical determination of the properties of nitrogen that are relevant in metrology. Here we present first-principles calculations of the temperature and frequency dependence of the molecular polarizability and magnetic susceptibility of the nitrogen molecule (N$_2$). The purely electronic contributions to the static polarizability, Cauchy coefficients (up to sixth order), and isotropic magnetic susceptibility are computed over a range of internuclear distances using a robust composite scheme combining several electronic structure methods. The temperature dependence, evaluated from $50$~K to $2000$~K, is determined using two independent methods: rovibrational averaging and path integral Monte Carlo (PIMC). The polarizabilities obtained from theory agree with the recent high-precision thermometry measurements, wherever the latter are available, but are significantly less accurate. However, the main usefulness of the theoretical data revolves around combining it with the available experimental results to generate semi-empirical estimates of various quantities that have never been measured thus far. As an example, we determine highly accurate semi-empirical estimates of the static polarizability at key reference temperatures, $α_0(T)=11.735\,962$~a.u.\ at $T=303$~K and $α_0(T)=11.735\,585$~a.u.\ at $T=273.16$~K. Furthermore, we report theoretical values for the magnetic susceptibility, highlighting the importance of the paramagnetic contribution, and address a significant discrepancy with the experimental data for this quantity.
