[18]Annulene的结构重新审视:计算类系统的挑战
Rollin A King1, Peter R Schreiner2, T Daniel Crawford3
1Department of Chemistry, Bethel University, St. Paul, Minnesota 55112, United States.
The journal of physical chemistry. A
|February 2, 2024
概括
像Hartree-Fock (HF) 和密度函数理论 (DFT) 这样的计算化学方法对于循环联系统可以产生不可靠的结果. 这项研究揭示了接近零的分子轨道 (MO) 稳定性固有值,而不是负值,导致振动频率的重大错误.
科学领域:
- 计算化学是一种计算化学.
- 量子化学是一种量子化学.
- 理论化学是一种理论化学.
背景情况:
- 哈特里-福克 (HF) 和密度函数理论 (DFT) 方法经常产生周期性并联系统的不稳定的计算结果,特别是那些高HF交换贡献的系统.
- 这种不可靠性源于与分子轨道 (MO) 稳定性相关的问题,特别是接近零的固有值.
研究的目的:
- 探索循环并联结构计算方法不可靠的原因.
- 为避免陷提供指导,并在对此类系统的计算调查中确保尽职调查.
- 为了确定[18]annulene的平衡结构.
主要方法:
- 对[18]annulene和相关化合物的广泛计算.
- 仔细检查MO单元稳定性固有值.
- 密度安装的冷自然轨道合集群单个和双重与扰动三重 (DF-FNO CCSD(T)) 方法使用aug-pVQZ/aug-pVTZ基础集.
主要成果:
- 接近零的 (正或负) MO单元稳定性固有值,而不是负的,可以导致振动频率和相关属性的戏剧性错误.
- 低HF添加剂的DFT方法通常对类结构更为稳健,但可能会高估平面性和C-C键均等.
- [18]烯表现出非平面平衡结构,发现全球C2最小值低于D6静止点的1.1 kcal mol-1.
结论:
- 对MO单元稳定性固有值的彻底检查对于循环并联系统的可靠计算研究至关重要.
- 虽然低HF交换的DFT往往更稳定,但它可以引入偏差.
- [18]annulene的平衡结构是非平面的,这是由高层相关计算所支持的.
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