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探索NMR旋转-旋转合常数的高水平振动校正计算的替代方法

Ronan Gleeson¹, Patrick A Aggelund¹, Frederik C Østergaard¹

¹Department of Chemistry, University of Copenhagen, 2100 Copenhagen, Denmark.

Journal of chemical theory and computation

|February 1, 2024

概括

本研究介绍了一种成本效益高的方法,用于计算核磁共振 (NMR) 旋转-旋转合常量 (SSCC) 中的核运动校正. 结合集群单双 (CCSD) /B3LYP方法为这些基本的NMR参数提供了最佳的准确性和计算效率.

科学领域:

计算化学计算化学
量子化学是一个量子化学.
频谱学是一种光谱学.

背景情况:

传统的核磁共振 (NMR) 计算通常忽略了核运动,使用固定的核几何.
核运动可以通过对振动波函数的平均属性来解释,并对平衡几何值添加修正.
精确计算振动校正是计算密集的,限制了它们的常规应用.

研究的目的:

通过振动二次扰动理论 (VPT2) 对旋转-旋转合常量 (SSCC) 的振动校正进行合集群单双 (CCSD) 的基准测试.
探索计算上更便宜的电子结构方法来计算这些振动校正.
为了确定振动纠正SSCC的精度和计算成本之间的最佳平衡.

主要方法:

使用结合集群单双 (CCSD) 的基准计算与振动校正的CCSD (T) 近似.
在达尔顿项目中开发和应用一个用于振动平均的Python程序.
用包括二次极化传播器近似 (SOPPA) 和密度函数理论 (DFT) 在内的方法比较CCSD//CCSD(T) 结果,使用B3LYP和PBE0函数.

主要成果:

CCSD//CCSD (T) 计算提供了与实验SSCC的有利协议,但在计算上昂贵.
CCSD//CCSD(T) + B3LYP方法的准确性 (平均绝对偏差) 与更昂贵的CCSD//CCSD(T) 方法相似.
更高层次的CC3//CCSD(T) + CCSD//CCSD(T) 计算显示,与实验值的一致性有所恶化,这可能是由于基础设置的限制或缺乏解决.

结论:

CCSD//CCSD(T) + B3LYP方法被认为是计算SSCC振动校正的最佳方法,平衡成本和准确性.
对于许多经过测试的方法,振动校正的计算成本与实验值相比,精度的提高并不合理.
未来的高层计算应考虑基数效应和解法,以提高准确性.

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