Ethenedithione (S=C=C=S): Does It Obey Hund's Rule?

Significantly higher in energy (24 kJ mol⁻¹) than the triplet ground state (³Σ_g⁻) is the ¹Δ_g state of ethenedithione (S=C=C=S), in agreement with Hund's rule. This result was obtained from high-level ab initio calculations. Thus, ethenedithione cannot, as had been proposed, be considered as the first example for the violation of Hund's rule in an equilibrium structure.     

Reactions of Selected Bismuth Oxide Cluster Cations with Propene

Bismuth oxide cluster ions are reduced by propene in exactly the same way as solid bismuth oxide (Bi₂O₃), which is used as a catalyst. Even in the case of the smallest bismuth oxide cluster ions, such as the Bi₃O₄⁺ isomer shown in the picture, the supposedly unreactive bridging oxygen atom can participate in the alkene oxidation.     

The Cluster Anion Si94−

Solely on the basis of Raman spectra and quantum chemical calculations, the previously unknown cluster anion Si₉⁴⁻ (structure shown) was characterized and its structure determined. The anion is formed as a component of solid phases by the thermal decomposition of alkali metal monosilicides.     

Organic Dications: Gas Phase Experiments and Theory in Concert

Knowledge of structure and bonding are integral parts in the understanding of the chemistry of neutral, radicaloid and positively or negatively charged species. The interplay of molecular bonding and the inherent electrostatic repulsion in doubly-charged molecules expands our insight in the versatility of bonding in electron deficient molecules. Small organic dications are now routinely detected in the gas phase by a variety of mass spectrometric techniques. Ab initio molecular orbital theory has advanced to the stage of accurately predicting potential energy surfaces. This review highlights the symbiotic relationship between gas-phase ion and computational studies and gives a rationale for the salient bonding features in doubly-charged organic cations.     

LiAl的电子与几何结构

应用平面波展开和第一原理赝势法研究了锂铝单晶的电子和几何结构,给出LiAl各种可能结构的能量～体积关系图以及相关的能带结构,电子态密度和电荷密度分布等各种性质变化关系.讨论了B32结构与其他结构电子键合性质的不同,指出B32结构之所以成为LiAl最稳定的结构是由于Al＿Al原子形成了类似于Si＿Si的共价键合.计算得到的能量最低的稳定结构与实验以及其它的理论计算结果一致.     

Structural transition of NaBH4 under high pressure: Ab initio calculations

The pressure induced structural transition of NaBH₄ from β-NaBH₄ (tetragonal-P42_1c) to γ-NaBH₄ (orthorhombic-Pnma) is investigated by ab initio plane-wave pseudopotential density functional theory method (DFT). The BaSO₄-type structure of orthorhombic high-pressure phase is testified theoretically for the first time. The calculated transition pressure of β-NaBH₄ (tetragonal-P42_1c) to γ-NaBH₄ (orthorhombic-Pnma) is 9.66 GPa and the orthorhombic high-pressure phase is stable up to 30 GPa. Our results agree well with previous experimental results and demonstrate that high-pressure phase transition from β-NaBH₄ to γ-NaBH₄ may occur at low temperature. At last, the pressure effects on the electronic structures of α-, β- and γ-NaBH₄ are discussed.     

新金刚石电子结构的第一性原理研究

金刚石、 石墨和卡宾碳是三种常见的碳同素异构体, 其外层轨道价电子分别是以sp³-, sp²-和sp¹-形式杂化而成的^［1］. 1991年, Hirai等^［2］在研究金刚石的形成机理时, 发现了一种新的碳同素异构体, 并将其命名为新金刚石(new diamond) ^{［3, 4］}. 在许多实验过程中虽然也曾获得过新金刚石^［5~11］, 但是这些实验获得的新金刚石的样品产量都较少, 且新金刚石的颗粒尺寸都很小(小于100 nm), 因此只能采用电子衍射(ED)的方法研究其结构. Jarkov等^［9］在分析多晶体ED图谱的基础上, 认为新金刚石是面心立方结构(FCC), 其晶格常数为0.357 nm. 2001年, Konyashin等^［1］通过ED图谱、电子能量损失谱和半经验的能量计算认定新金刚石为FCC的纯碳, 其晶格常数为0.356 3 nm. 我们曾用强磁场碳黑催化法制备出大量的新金刚石^{［3,4,12~14］}, 并对新金刚石的热稳定性进行了研究^［12］, 而对其结构和性能的研究尚未见报道.     

Anharmonic vibrational spectroscopy calculations with electronic structure potentials: comparison of MP2 and DFT for organic molecules

Density functional theory (DFT) technique is the most commonly used approach when it comes to computation of vibrational spectra of molecular species. In this study, we compare anharmonic spectra of several organic molecules such as allene, propyne, glycine, and imidazole, computed from ab initio MP2 potentials and DFT potentials based on commonly used BLYP and B3LYP functionals. Anharmonic spectra are obtained using the direct vibrational self-consistent field (VSCF) method and its correlation-corrected extension (CC-VSCF). The results of computations are compared with available experimental data. It is shown that the most accurate vibrational frequencies are obtained with the MP2 method, followed by the DFT/B3LYP method, while DFT/BLYP results are often unsatisfactory. Contribution to the Mark S. Gordon 65th Birthday Festschrift Issue.