Analytic atomic gradients in the fermi-löwdin orbital self-interaction correction

We derived, implemented, and thoroughly tested the complete analytic expression for atomic forces, consisting of the Hellmann-Feynman term and the Pulay correction, for the Fermi-Löwdin orbital self-interaction correction (FLO-SIC) method. Analytic forces are shown to be numerically accurate through an extensive comparison to forces obtained from finite differences. Using the analytic forces, equilibrium structures for a small set of molecules were obtained. This work opens the possibility of routine self-interaction free geometrical relaxations of molecules using the FLO-SIC method. © 2018 Wiley Periodicals, Inc.     

Density functional crystal vs. cluster models as applied to zeolites

In order to compare solid and cluster models of zeolites, we have studied the substitution Si⁴⁺→Al³⁺+H⁺ on the T₁ site of mordenite in the dilute limit using a self-consistent, full potential, local density functional (LDF) approach. Clusters size ranged from 9 to 105 atoms. Two crystal models with different Al concentrations were used. The first contained one substitution site per primitive cell of 72 atoms, the other one per conventional cell, containing 144 atoms. The unrelaxed substitution energies as computed with cluster and crystal models correspond well if the cluster results are extrapolated to infinite radius. Size effects are much smaller in crystal models. In addition, a structure relaxation (with fixed unit cell) was carried out for pure-silica offretite, a zeolite with 54 atoms per unit cell, and pure-silica mordenite, with 144 atoms per unit cell, starting from the low aluminum content X-ray crystallographic structure. In the offretite and mordenite optimizations full use was made of the D_3h¹–P $ \bar 6 $m2 and the nonsymmorphic D_2h¹⁷–Cmcm space group symmetry, respectively. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 135–144, 1998     

PCM study of the solvent and substituent effects on bond dissociation energies of the C?NO bond

Quantum chemical calculations are used to estimate the equilibrium C? NO bond dissociation energies (BDEs) for eight X? NO molecule (X = CCl₃, C₆F₅, CH₃, CH₃CH₂, iC₃H₇, tC₄H₉, CH₂CHCH₂, and C₆H₅CH₂). These compounds are studied by employing the hybrid density functional theory (B3LYP, B3PW91, B3P86) methods together with 6‐31G** and 6‐311G** basis sets and the complete basis set (CBS‐QB3) method. The obtained results are compared with the available experimental results. It is demonstrated that B3P86/6‐31G** and CBS‐QB3 methods are accurate for computing the reliable BDEs for the X? NO molecule. Considering the inevitably computational cost of CBS‐QB3 method and the reliability of the B3P86 calculations, B3P86 method with 6‐31G** basis set may be more suitable to calculate the BDEs of the C? NO bond. The solvent effects on the BDEs of the C? NO bond are analyzed and it is shown that the C? NO BDEs in a vacuum computed by using B3PW91/6‐311G** method are the closest to the computed values in acetontrile and the average solvent effect is 1.48 kcal/mol. Subsequently, the substituent effects of the BDEs of the C? NO bond are further analyzed and it is found that electron denoting group stabilizes the radical and as a result BDE decreases; whereas electron withdrawing group stabilizes the group state of the molecule and thus increases the BDE from the parent molecule. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

密度泛函方法研究噻唑橙类菁染料的光谱性质

4-(二乙基氨基)丁基取代的三甲川噻唑橙(DEAB-TO3)具有极低的本底荧光可用于核酸检测。本文运用密度泛函理论研究了4-(二乙基氨基)丁基取代的一甲川噻唑橙(DEAB-TO1)和DEAB-TO3光谱性质。基态和激发态几何优化显示激发态构型高度扭曲;光谱计算和轨道分析得出第一激发态是暗态,出现了扭曲的分子内电荷转移;势能曲线计算可知,DEAB-TO1和DEAB-TO3有着极低的能隙和旋转能垒。以上结果解释了本底荧光极弱的实验现象。     

Si4X(X=C,N,O,Si,P,S)原子簇结构的理论研究

在密度泛函B3LYP/6-311G*水平上, 对具有C3v对称的Si4X (X = C, N, O, P, S)原子簇进行了几何构型优化计算, 并讨论它们的热力学稳定性、动力学活性、Mulliken布居、SiX键长、占据价轨道的对称性以及HOMO能级位置等周期递变规律。     

Water Oxidation for Simplified Models of the Oxygen‐Evolving Complex in Photosystem II

For the main parts of the mechanism for water oxidation in photosystem II there has recently been very strong experimental support for the mechanism suggested by theoretical model studies. The question addressed in the present study is to what extent this knowledge can be used for the design of artificial catalysts. A major requirement for a useful artificial catalyst is that it is small enough to be synthesized. Small catalysts also have the big advantage that they could improve the catalysis per surface area. To make the mechanism found for PSII useful in this context, it needs to be analyzed in detail. A small model system was therefore used and the ligands were replaced one by one by water‐derived ligands. Only the main chemical step of O?O bond formation was investigated in this initial study. The energetics for this small model and the larger one previously used for PSII are remarkably similar, which is the most important result of the present study. This shows that small model complexes have a potential for being very good water oxidation catalysts. It was furthermore found that there is a clear correlation between the barrier height for O?O bond formation and the type of optimal structure for the S₃ state. The analysis shows that a flexible central part of the complex is the key for efficient water oxidation.     

烷基吡啶及氯化铝正负离子结构的密度泛函研究

采用量子化学密度泛函方法对N-烷基吡啶阳离子和阴离子AlCl4-,Al2Cl7-和Al3Cl10-进行了全优化计算,得到了阴阳离子的几何构型和净电荷分布.计算发现,吡啶环上的电子数符合4n 2规则,具有芳香性.吡啶阳离子的LUMO轨道主要由环上原子的2pz所贡献,是反键π分子轨道.AlCl4-,Al2Cl7-和Al3Cl10-的HOMO轨道主要由Cl原子的2px所贡献.推测吡啶阳离子的LUMO与阴离子的HOMO相互作用形成离子液体分子.     

硝酰氯和顺/反亚硝酸氯及其互变异构反应的理论研究

用密度泛函理论（DFT）的B3LYP方法和6－311＋G（3df）基组，计算了气态下硝酰氯和顺／反应硝酸氯的几何构型、电子结构、红外光谱以及热力学性质，并讨论了它们的互变异构反应，分析了过渡态的结构。结果表明，B3LYP／6－311＋G（3df）计算得到的结果与实验值及CCSD（T）方法计算结果吻合，且更适应于研究反应机理，ClNO2转变为cis-ClONO的过渡态（TS1）偏离平面构型；cis-ClONO和trans-ClONO互变反应的过渡态（TS2）属于内旋转位垒；高水平计算表明不存在由ClNO2直接转变为trans-ClONO的过渡态，而是得到了一个十分接近异裂产物的二级马鞍点（2SP）。根据得到的热力学函数计算了气态时各温度下互变异构反应的平衡常数。     

Is it worthwhile to go beyond the local-density approximation in subsystem density functional theory?

Frozen density embedding (FDE) theory is one of the major techniques aiming to bring modeling of extended chemical systems into the realm of high accuracy calculations. To improve its accuracy it is of interest to develop kinetic energy density functional approximations specifically for FDE applications. In the study reported here we focused on optimizing parameters of a generalized gradient approximation-like kinetic energy functional with the purpose of better describing electron excitation energies. We found that our optimized parametrizations, named excPBE and excPBE-3 (as these are derived from a Perdew-Burke-Ernzerhof-like parametrization), could not yield improvements over available functionals when applied on a test set of systems designed to probe solvatochromic shifts. Moreover, as several different functionals yielded very similar errors to the simple local-density approximation (LDA), it is questionable whether it is worthwhile to go beyond the LDA in this context.