卤化钙钛矿太阳能电池材料理论研究进展

卤化钙钛矿由于具有低成本、高效率等特点,最近作为非常有前景的太阳能电池吸收层材料被广泛研究。卤化钙钛矿型太阳能电池效率在短短的几年间由3.8%(2009年)迅速增加到22.1%(2016年)。卤化钙钛矿型太阳能电池的出现彻底改变了太阳能电池领域,不仅因为它们快速增长的效率,而且因为它们在材料生长和结构方面的可控性。卤化钙钛矿型太阳能电池的优越性能说明卤化钙钛矿材料具有独特的物理性质。在本综述中,我们总结了卤化钙钛矿材料最近几年在结构、电学、光学方面的理论研究成果,这些都与它们在太阳能电池方面的应用密切相关。我们也将探讨一些卤化钙钛矿型太阳能电池目前遇到的挑战以及可能的理论解决途径。     

Why calcium inhibits magnesium-dependent enzyme phosphoserine phosphatase? A theoretical study

Mechanisms for the formation of the Schiff base from acetaldehyde and butylamine, glycine and phosphatidylethanolamine based on Dmol3/DFT calculations were realized. For the case of phosphatidylethanolamine, calculations were done under periodic boundary conditions, in an amine-phospholipid monolayer model with two molecules of phosphatidylethanolamine by cell. All models contained explicit aqueous solvent. In the three cases, a neutral amino group is used to model the nucleophilic attack on the carbonyl group of acetaldehyde, and water molecules form hydrogen bond networks. These networks were involved in the reactions by performing as proton-transfer carriers, important in some steps of reactions, and stabilizing reaction intermediates. In all the studied reactions, they take place in two steps, namely: (1) formation of a carbinolamine and (2) its dehydration to the Schiff base, being the dehydration the rate-determining step of the process, consistent with available experimental evidence for similar reactions. The main difference between the studied reactions is found in the value for relative free energy for the intermediates and transition states in the second step; these values are lower in the cases of glycine and phosphatidylethanolamine in comparison with butylamine, due the influence of their molecular environments. Based on the results, the aminophospholipid surface environment and carboxylic group of glycine may boost Schiff base formation via a neighboring catalyst effect.     

Possible effects of oxygen in Te-rich Σ3 (112) grain boundaries in CdTe

Using density functional theory calculation, we show that oxygen (O) exhibits an interesting effect in CdTe. The Te atoms with dangling bonds in a Te-rich rich Σ3 (112) grain boundary (GB) create deep gap states due to strong interaction between Te atoms. However, when such a Te atom is substituted by an O atom, the deep gap states can be shifted toward the valence band, making the site no longer a harmful non-radiative recombination center. We find that O atoms prefer energetically substituting these Te atoms and induce significant lattice relaxation due to their smaller atomic size and stronger electronegativity, which effectively reduces the anion–anion interaction. Consequently, the deep gap states are shifted to lower energy regions close to or even below the top of the valence band.     

硫代樟脑光化学反应的理论研究

运用量子化学方法优化了硫代樟脑的最低5个电子态(S₀, T₁, S₁, T₂和S₂)的结构, 并计算了它们的相对能量. 计算结果表明: S₁, T₁和T₂态的能量非常接近, 而S₂的能量远远高于T₂态, 这与之前对几种小的硫代羰基化合物的研究结论一致. 确定了硫代樟脑分子在T₁态发生β-插入反应和类Norrish II型反应的机理, 计算的势垒相对于S₀的振动零点分别为314.1和332.6 kJ/mol. 在400 nm波长的光的照射下, 分子被激发到S₁态, 此时分子没有足够的能量发生反应, 只能通过内转换回到基态. 当激发光波长在254 nm时, 硫代樟脑分子被激发到S₂态, 这时候体系有了足够的内部能量使反应发生. 实验上已经观察到此激发光波长下, 气态硫代樟脑可以发生β-插入反应和类Norrish II型反应.     

硫代乙酰胺光化学反应机理的理论研究

用B3LYP, MP2和CASSCF方法, 采用cc-pVDZ和6-31++G**基组, 研究了硫代乙酰胺在基态和最低三态上消除硫化氢以及其它光解离反应, 并考虑了单个溶剂分子参与反应对质子迁移反应的影响, 得到了消除硫化氢反应的反应机理, 计算结果可以很好地解释实验结果. 进而用CASSCF方法计算了第一激发单态上的各驻点, 以及各交叉点. 计算结果表明, 在S1和T1态上发生除分子内转动以外的化学反应的可能性比较小, 当分子被激发到S2态上时, 将通过S2/S1交叉点到S1态, 在S1态上的分子有两条途径去活化, 通过S1/S0交叉点到热基态, 通过S1/T1交叉点系间窜越到T1态. 因而得出CH3CSNH2发生光解离反应的可能性不大. 基于此, 可将硫代酰胺结构引入蛋白或多肽中, 有望在不破坏分子整体结构的情况下对其进行光化学研究.     

Double-hole-mediated coupling of dopants and its impact on band gap engineering in TiO2

A double-hole-mediated coupling of dopants is unraveled and confirmed in TiO2 by density-functional theory calculations. We find that when a dopant complex on neighboring oxygen sites in TiO2 has net two holes, the holes will strongly couple to each other through significant lattice relaxation. The coupling results in the formation of fully filled impurity bands lying above the valence band of TiO2, leading to a much more effective band gap reduction than that induced by monodoping or conventional donor-acceptor codoping. Our results suggest a new path for semiconductor band gap engineering.     

Defect calculations with quasiparticle correction: A revisited study of iodine defects in CH3NH3PbI3

Defect levels in semiconductor band gaps play a crucial role in functionalized semiconductors for practical applications in optoelectronics;however,first-principle defect calculations based on exchange-correlation functionals,such as local density approximation,grand gradient approximation(GGA),and hybrid functionals,either underestimate band gaps or misplace defect levels.In this study,we revisited iodine defects in CH₃NH₃PbI₃ by combining the accuracy of total energy calculations of GGA and single-electron level calculation of the GW method.The combined approach predicted neutral Im_i to be unstable and the transition level of Im_i(+1/-1)to be close to the valence band maximum.Therefore,Im_i may not be as detrimental as previously reported.Moreover,Vm I may be unstable in the-1 charged state but could still be detrimental owing to the deep transition level of Vm I(+1/0).These results could facilitate the further understanding of the intrinsic point defect and defect passivation observed in CH₃NH₃PbI₃.     

Hybridized kinetic energy functional for orbital-free density functional method

We propose a hybridized kinetic energy functional, aTTF+bTvW, where TTF is the Thomas-Fermi functional and TvW the von Weizsäcker functional while a and b are adjustable parameters. The new functional is implemented in orbital-free plane-wave density functional method, in which a conjugate-gradient line-search scheme of electronic minimization is incorporated. Calculations with the fitted a and b show that this kinetic energy functional can describe the structures of small Si, Al and Si-Al alloy clusters with reasonable accuracy.     

两种4’-对甲苯磺酰基异黄酮衍生物的合成及抗氧化性质研究

摘要 合成了未见文献报道的脂溶性较好的7-甲氧基-4’-对甲苯磺酰基异黄酮（L1）和7-氧乙酸乙酯-4’-对甲苯磺酰基异黄酮（L2）,并得到了L1的单晶结构,采用IR、1H NMR、元素分析和X射线单晶衍射对L1进行了结构表征. 利用紫外分光光度法研究了化合物L1和L2对DPPH•自由基的清除作用,并采用量子化学半经验法（AM1）和Hartree-Fock 从头算的方法,计算了化合物分子中相关原子的电荷密度,探讨了它们与DPPH•自由基反应的可能活性位点. 获得了理论计算和光谱实验相一致的结果. 晶体结构测定表明, L1晶体属单斜晶系,P2 (1)/c点群, a=20.041(5)Å ,b=6.0876(17)Å ,c=16.516(4)Å. 理论推断和光谱实验表明,L2对DPPH自由基的清除效果好于L1.     

Theoretical studies on pyridoxal 5'-phosphate-dependent transamination of alpha-amino acids

Density functional methods have been applied to investigate the irreversible transamination between glyoxylic acid and pyridoxamine analog and the catalytic mechanism for the critical [1,3] proton transfer step in aspartate aminotransferase (AATase). The results indicate that the catalytic effect of pyridoxal 5'-phosphate (PLP) may be attributed to its ability to stabilize related transition states through structural resonance. Additionally, the PLP hydroxyl group and the carboxylic group of the amino acid can shuttle proton, thereby lowering the barrier. The rate-limiting step is the tautomeric conversion of the aldimine to ketimine by [1,3] proton transfer, with a barrier of 36.3 kcal/mol in water solvent. A quantum chemical model consisting 142 atoms was constructed based on the crystal structure of the native AATase complex with the product L-glutamate. The electron-withdrawing stabilization by various residues, involving Arg386, Tyr225, Asp222, Asn194, and peptide backbone, enhances the carbon acidity of 4'-C of PLP and Calpha of amino acid. The calculations support the proposed proton transfer mechanism in which Lys258 acts as a base to shuttle a proton from the 4'-C of PLP to Calpha of amino acid. The first step (proton transfer from 4'-C to lysine) is shown to be the rate-limiting step. Furthermore, we provided an explanation for the reversibility and specificity of the transamination in AATase.