Surfaces and interfaces in short-period GaAs/AlAs superlattices

Photoelectron spectroscopy, in particular the angular resolved photoemission excited by ultraviolet radiation (ARUPS), provides the most direct experimental information about the electron structure of crystals, both of the bulk and of the low-index surfaces. The sensitivity of the method, as well as its difficulties, when applied to GaAs/AlAs superlattices are described. The new periodicity of these man-made crystals in the direction of their growth (e.g., in the layer-by-layer growth in molecular beam epitaxy), is responsible for opening of the new energy gaps (so-called minigaps) in the electron energy bands of crystals forming the superlattice. In addition to the well-known confinement of electrons at the valence and conduction band edges in long-period superlattices, the electron confinement to the interfaces has also been found in the vicinity of minigaps in short-period superlattices. The role of this confinement in the intensities of electrons photoemitted from superlattice surfaces is discussed. Superlattices with different thicknesses in the topmost layers represent systems with a simple change of the surface atomic structure. The predictions of one-dimensional models about a change of the surface-state energy within the band gap with a change of crystal potential termination are tested for the ideally terminated (1 0 0) surface of a very thin superlattice (GaAs)₂(AlAs)₂. The results of the energy distributions of photoemitted electrons, calculated in the one-step model of photoemission, show that the ARUPS experimental observation of surface-state shifts should be possible, at least in larger minigaps. The results indicate the possibility of a straightforward tuning of the electronic structure of the superlattice surface by geometrical means.     

Comparison of the effective core potential and model potential methods in studies of electron correlation energy in molecules: Dihalides and halogen hydrides

Summary The effective core potential and model potential methods were used in post-SCF calculations on HC1, HBr, Cl₂, and Br₂ in order to gain insight into the effect of insufficient representation of inner nodes in the valence orbitals of the approximate methods. The results show that while the correlation energy may be slightly overestimated (by 1–7%), both the electric moment functions and the quantities depending on energy differences are consistently similar for the methods studied and close to the results from all-electron calculations.Dedicated to Prof. Klaus Ruedenberg     

Electron-transfer in molecular functional materials

We discuss electron-transfer processes that govern the physics of several materials or systems of interest for advanced applications. The discussion touches upon several topics, ranging from solvatochromism to solvent-induced symmetry breaking, from excitonic to cooperative effects in molecular crystals, from phase transitions to vibrational contributions to the dielectric constant in organic materials, from spectroscopy to molecular transport. In all these diverse systems electron transfer (ET) plays a major role and is discussed with reference to simple models for delocalized charges.     

氟化镁锶中铕和铽的电荷迁移及其平衡解析

在氩气氛中，合成子ＳｒＭｇＦ４：ｘＥｕ，ｙＴｂ复合氟化物磷光体，该体系中Ｅｕ＾３＋和Ｅｕ＾２＋共存，随共掺入Ｔｂ浓度的增加，Ｅｕ＾３＋的荧光发射强度降低，Ｅｕ＾３＋的发光增强，并且Ｅｕ＾２＋的ＥＳＲ信号增强，认为Ｅｕ＾３＋和Ｔｂ３＋之间存在的电荷迁移，即Ｅｕ＾３＋Ｔｂ＾３＋→Ｅｕ＾２＋＋Ｔｂ＾４＋，通过半量手段研究了这一电荷迁移反应的平衡常数。     

A perylenedicarboxamide linker for DNA hairpins

The synthesis and properties of a perylenediamide diol linker and several DNA hairpins possessing this linker are described. The diol linker absorbs and fluoresces strongly in the visible. Hairpins having poly(dA)-poly(dT) stems have fluorescence quantum yields and decay times similar to those of the linker, indicating that hole injection does not occur from the singlet excited linker into the base pair domain. Fluorescence quenching by dG or dZ bases is observed when these bases are located near the linker. The strong distance dependence of fluorescence quenching is consistent with a superexchange mechanism for electron transfer. Failure to observe formation of the linker anion radical by means of femtosecond time resolved absorption spectroscopy is attributed to fast charge recombination. The properties and behavior of the perylene linker and its hairpins are compared to those of other arenedicarboxamide linkers.     

Charge transfer and electron backdonation in metallofullerenes encapsulating NSc3

Orbital interaction analysis is employed to understand the complex charge transfer mechanism operative in endohedral metallofullerenes of composition NSc₃@C_n (n = 68, 78). This phenomenon combines substantial electron transfer from the core to the cage with electron backdonation, involving the interaction between the occupied orbitals of the negatively charged cage and the unoccupied d orbitals of the positively charged core. This electron backdonation differs fundamentally from conventional orbital hybridization, which takes place primarily between the HOMO of the metal core and the LUMO of the fullerene cage. These findings imply the pronounced stability of NSc₃@C_n (n = 68, 78), especially for NSc₃ encapsulated in the non-IPR C₆₈ enclosure, as experimentally established.     

卟啉酞菁模型化合物光致电子转移研究

本文采用时间相关单光子计数对卟啉酞菁ＴＴＰ－（ＣＨ２）ｎ－Ｐｃ模型化合物的光致电子转移进行了研究，发现激发Ｐｃ时，呈现单指数衰减，ｎ＝４时电子转移速率减小，活化能，重排能增加，电子转移效率下降，电子转移反应△ＧＣＳ与电荷分离活化络合物衰变速率ＫＣＴ，按以下规律：△Ｇ＾（５）ＣＳ〉△＾（３）ＣＳ〉△＾（４）ＣＳ〉△＾（２）ＣＳ，ｋ＾（２）ＣＳ〉ｋ＾（３）ＣＳ〉ｋ＾（４）ＣＳ〉ｋ＾（５）ｃｓ。其△Ｇ＾     

On the accuracy of correlation energy calculated by the correlation factor method: first- and second-row atoms

Summary The correlation energy of two- and four-isoelectronic series, a representative example for which the existing spin-density functionals fails, is calculated using the Colle and Salvetti method, considering mono- and multideterminantal wave functions. The results are in agreement with experimental data, and show the potentiality of this method when it is applied to wave functions including the most relevant configurational features. Also, results for the ionization energies and electron affinities of first- and second-row atoms are reported.     

[Fe4S4Cl4—n（S2CNEt2）n]^2—（n=0,1,2,4）：原子簇的电子结构研究

用CNDO/2(s,p,d)方法研究了类立方烷系列Fe-S簇合物[Fe_4S_4Cl_4(?)(S_2CNEt_2)_n]~(2-)(n=0,1,2,4)的电子结构。得出[S_2CN(Et)_2]-螯合配位Fe_4S_4~(2+)簇合物中存在两类不同价态铁原子的结论;骨架Fe_4S_4~(2+)中μ_3-S电子是非定域化的,同Mssbauer谱测定结果一致。讨论了簇合物Fe—Fe之间的成键作用、螫合配体的作用和氧化还原性质。