Assessment and formal properties of exchange-correlation functionals constructed from the adiabatic connection

We examine the development and investigate the performance of exchange-correlation functionals constructed from the adiabatic connection. Our method is based on a direct modeling of the adiabatic connection curve in the coupling-constant space and is very flexible in the models. Several different models are investigated in the construction of new families of exchange-correlation functionals. Also the performance of two of these models (MCY1 and MCY2) is investigated over a wider range of systems and properties, with comparison made to the performance of established functionals. Overall, the adiabatic functionals improve upon widely used hybrid and generalized gradient approximation functionals, particularly in correctly describing one-electron systems and reaction energy barriers.     

Nature of the band gap and origin of the conductivity of PbO2 revealed by theory and experiment

Lead dioxide has been used for over a century in the lead-acid battery. Many fundamental questions concerning PbO2 remain unanswered, principally: (i) is the bulk material a metal or a semiconductor, and (ii) what is the source of the high levels of conductivity? We calculate the electronic structure and defect physics of PbO2, using a hybrid density functional, and show that it is an n-type semiconductor with a small indirect band gap of ～0.2 eV. The origin of electron carriers in the undoped material is found to be oxygen vacancies, which forms a donor state resonant in the conduction band. A dipole-forbidden band gap combined with a large carrier induced Moss-Burstein shift results in a large effective optical band gap. The model is supported by neutron diffraction, which reveals that the oxygen sublattice is only 98.4% occupied, thus confirming oxygen substoichiometry as the electron source.     

Cu2ZnSnS4类四元硫族半导体的理论研究——以二元、三元、四元半导体的演化为思路

在过去60多年中,人们对半导体的研究集中在一元、二元和三元半导体方面,最近,出于寻找新型廉价、环保、高效光伏转换材料的需要,Cu2ZnSnS4类Ⅰ2-Ⅱ-Ⅳ- Ⅵ4型四元硫族半导体吸引了人们越来越多的关注,它在光催化和热电等多方面的应用也不断被发掘.然而,对于这类四元半导体的基本性质,如晶体结构和电子结构,人们知之甚少,很多研究还停留在经验阶段.文章首先简要回顾了这类半导体的由来和在应用方面的最新进展,然后详细介绍了文章作者对这类四元半导体的第一性原理计算研究工作的进展,其中包括:系统研究了这类硫族半导体在从二元向三元再向四元的演化过程中晶体结构和电子能带结构变化的规律,总结了元素成分对其影响的一般趋势,并结合实验结果分析了这类四元半导体晶格结构表征和带隙测量中易于出现的混淆;文章作者还以Cu2ZnSnS4为例,考察了这类四元化合物相对二元、三元化合物的相稳定性和本征缺陷性质.文章介绍的研究结果将为一系列Ⅰ2-Ⅱ-Ⅳ- Ⅵ4型四元半导体的深入研究提供基础.     

Homology of homogeneous divisors

This work deals with arbitrary reduced free divisors in a polynomial ring over a field of characteristic zero, by stressing the ideal theoretic and homological behavior of the corresponding singular locus. A particular emphasis is given to both weighted homogeneous and homogeneous polynomials, allowing to introduce new families of free divisors not coming from either hyperplane arrangements or discriminants in singularity theory.     

The equations of almost complete intersections

In this paper we inject four Hilbert functions in the determination of the defining equations of the Rees algebra of almost complete intersections of finite co-length. Because three of the corresponding modules are Artinian, some of these relationships are very effective, with the novel approach opening up tracks to the determination of the equations and also to processes of going from homologically defined sets of equations to higher degrees ones. While not specifically directed towards the extraction of elimination equations, it will show how some of these arise naturally.     

Smooth Surjections Without Surjective Restrictions

Let f:E→F be a surjective mapping between two real or complex Banach spaces, with f having some strong differentiability properties. We investigate when there is a smaller Banach space G?E such that the restriction of f to G remains surjective.     

Use of central-field potentials for describing H2(D2) elastic scattering by other molecules

Differential elastic scattering cross sections have been measured for the systems H₂ + O₂, SF₆, NH₃, CO and CH₄ and for D₂ + O₂, SF₆, and NH₃ using crossed molecular beams. These experiments represent a wide variation in the size, anisotropy and initial relative collision energy E of the scattering partners, and of the corresponding de Broglie wavelengths. In all cases, rapid quantum oscillations have been resolved. From these differential cross sections, central-field potentials have been obtained which were independent of the energy and the isotopic composition of the hydrogen molecule used, as required for such potentials to be physically meaningful. Therefore, anisotropy effects do not seem important in describing the differential elastic scattering of these H₂(D₂) systems.     

THE REPAIR OF DNA STRAND BREAKS IN HUMAN LYMPHOCYTES EXPOSED TO NEAR UV-RADIATION (UVA) AND FAR UV-RADIATION (UVC)

Abstract— UVA irradiation of human lymphocytes induces DNA strand breaks and a portion of these breaks are closed at a slower rate than X-ray induced DNA strand breaks and the strand breaks generated during repair of UVC induced DNA lesions. In addition, the yield of DNA strand breaks in lymphocytes pretreated with UVA radiation and given a subsequent exposure with UVC radiation is higher and shows a slower decrease with increasing repair time in comparison with the expected yield based on additivity between UVA and UVC induced DNA strand breaks. This indicates that UVA delays the closure of the intermediate strand breaks formed in the repair process of UVC induced DNA lesions.     

ChemInform Abstract: Polymorph Engineering of TiO2: Demonstrating How Absolute Reference Potentials Are Determined by Local Coordination.

A multiscale quantum‐chemical approach is used for examining the electronic structure of eight known TiO₂ polymorphs and aligning their ionization potential and electron affinity relative to an absolute energy reference.