激发国家特定的CASSCF理论对乙烯扭曲
Sandra Saade1,2, Hugh G A Burton1
1Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K.
Journal of chemical theory and computation
|June 7, 2024
概括
国家特定的完全活跃空间自相一致场 (SS-CASSCF) 理论显示了激发状态计算的前景. 然而,非物理不连续性阻碍了其在计算光化学中的实际应用.
科学领域:
- 量子化学 是一个量子化学.
- 计算式光化学 计算式光化学
- 电子结构理论 电子结构理论
背景情况:
- 国家特定的完全活跃空间自相一致场理论 (SS-CASSCF) 是一种用于预测激发能量表面的发展方法.
- 它的准确性和适用于光化学系统的可行性需要进一步评估.
研究的目的:
- 评估SS-CASSCF理论对乙烯双键旋转的性能.
- 将SS-CASSCF与状态平均方法进行比较,并评估轨道优化效益.
主要方法:
- 使用SS-CASSCF研究低地面和乙烯的兴奋状态.
- 使用最小的 (2e,2o) 活动空间进行州特定的计算.
- 结果与使用更大的活跃空间的状态平均计算进行了比较.
主要成果:
- 使用最小活性空间的SS-CASSCF实现了与使用更大的空间的状态平均方法相比的准确性.
- 为每个兴奋状态优化轨道,增强波函数空间扩散性.
- 状态特定解决方案的错误排序导致了潜在能量表面的非物理不连续性.
结论:
- SS-CASSCF为激发状态计算提供了一个潜在的准确和高效的方法.
- 对于实际的计算光化学应用,必须解决理论上的挑战,特别是状态排序.
相关概念视频
01:12Cycloaddition Reactions: MO Requirements for Photochemical Activation
2.1K
Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
2.1K
01:17Thermal Electrocyclic Reactions: Stereochemistry
2.0K
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
2.0K
02:18Conformations of Ethane and Propane
13.9K
In an organic molecule, free rotation about the carbon-carbon single bond results in energetically different conformers of the molecule. Due to this rotation, called the internal rotation, ethane has two major conformations — staggered and eclipsed.
Staggered conformation is a low energy and more stable conformation with the C-H bonds on the front carbon placed at 60°dihedral angles relative to the C-H bonds on the back carbon, leading to a reduced torsional strain. In staggered...
Staggered conformation is a low energy and more stable conformation with the C-H bonds on the front carbon placed at 60°dihedral angles relative to the C-H bonds on the back carbon, leading to a reduced torsional strain. In staggered...
13.9K
01:26Photochemical Electrocyclic Reactions: Stereochemistry
1.8K
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
1.8K
02:11Conformations of Cyclohexane
12.4K
Cyclohexane does not exist in a planar form due to the high angle and torsional strain it would experience in the planar structure. Instead, it adopts non-planar chair and boat conformations.
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal...
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal...
12.4K
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
2.3K
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
2.3K