Heats of Formation for CrO, CrO2, and CrO3: An Extreme Challenge for Black-Box Composite Procedures.
Heats of Formation for CrO, CrO2, and CrO3: An Extreme Challenge for Black-Box Composite Procedures.
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CrO、CrO2 和 CrO3 的生成热：黑盒复合程序的极端挑战。
DOI：
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发表时间：
2012
影响因子：
5.5
通讯作者：
L. Radom
中科院分区：
文献类型：
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作者：
B. Chan;A. Karton;K. Raghavachari;L. Radom
在本研究中，我们使用复合方法，表示为CM（5）Λ和CM 5，后CCSD（T）项分别达到CCSDTQ（5）Λ和CCSDTQ 5，以评估CrO，CrO 2和CrO 3的原子化能。根据我们最佳估计的原子化能，生成热（ΔHf，298）为198.3 ± 5 kJ mol（-1）（CrO），-81.3 ± 5 kJ mol（-1）（CrO 2）和-286.8 ± 20 kJ mol（-1）（CrO 3）。标准G4型复合方法产生的原子化能量对于CrO是足够的，对于CrO 2不太好，对于CrO 3最不好。CrO 3是高度多参考的字符，因此，使用一个单一的参考RHF波函数的“黑箱”的方法是不够的，即使是“高层次”的G4型方法。我们发现，对于CrO 3，有一个非常大的差异，在G4原子化能量取决于是否使用RHF或UHF参考，这主要是与MP4组件的大的差异。在一般情况下，我们建议，一个大的R与U的差异很可能是一个潜在的问题，在理论治疗的指示。超越G4到更严格的基于UCCSD（T）的复合方案[在本研究中称为U-CM（3：[DZ，TZ]）]，我们再次发现基于RHF或UHF参考的CrO 3原子化能量之间存在很大差异（但明显小于G4）。有趣的是，使用Brueckner轨道作为所有组分的参考轨道，就像在相应的Brueckner Doubles（BD）程序[B-CM（3：[DZ，TZ]）]中一样，产生的CrO 3结果与使用RHF或UHF轨道作为起始点无关。
In the present study, we use composite methods, denoted CM(5)Λ and CM5, with post-CCSD(T) terms up to CCSDTQ(5)Λ and CCSDTQ5, respectively, to evaluate the atomization energies for CrO, CrO2, and CrO3. The heats of formation (ΔHf,298) based on our best estimated atomization energies are 198.3 ± 5 kJ mol(-1) (CrO), -81.3 ± 5 kJ mol(-1) (CrO2), and -286.8 ± 20 kJ mol(-1) (CrO3). Standard G4-type composite methods yield atomization energies that are adequate for CrO, less good for CrO2, and least good for CrO3. CrO3 is highly multireference in character, and therefore, a "black box" approach of using a single-reference RHF wave function is inadequate, even for "high-level" G4-type methods. We find that, for CrO3, there is a very large difference in the G4 atomization energies depending on whether an RHF or a UHF reference is used, which is mainly associated with large differences in the MP4 components. In general, we propose that a large R-versus-U difference is likely to be an indication of potential problems in the theoretical treatment. Going beyond G4 to a more rigorous UCCSD(T)-based composite scheme [termed U-CM(3:[DZ,TZ]) in the present study], we again find a large difference (but significantly smaller than that for G4) between the CrO3 atomization energies based on RHF or UHF references. Intriguingly, the use of Brueckner orbitals as reference orbitals in all components, as in the corresponding Brueckner Doubles (BD) procedure [B-CM(3:[DZ,TZ])], produces results for CrO3 that are independent of whether RHF or UHF orbitals are used as the starting point.