First-principle study on the electronic structure of stressed CrSi<Subscript>2</Subscript>

The electronic structure of stressed CrSi₂ was calculated using the first-principle methods based on plane-wave pseudo-potential theory. The calculated results showed that, under the uniaxial compression, the energy level of CrSi₂ shifted toward high energy and its energy gap became wider with the increasing uniaxial stress, while the gap became narrower under the negative uniaxial stress. When the negative uniaxial stress was up to −18.5 GPa, CrSi₂ was converted into a direct-gap semiconductor with the band gap of 0.32 eV. Supported by the National Natural Science Foundation of China (Grant No. 60566001), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050657003), the Scientific Research Foundation for the Returned Overseas Chinese Scholars, Ministry of Education of China (Grant No. (2005)383), the Program for the Excellent Young Talents of Guizhou Province (Grant No. 20050528), the Specialized Nomarch Research Fund for the Excellent Science and Technology and Education Talent’s Projects of Guizhou Province, Scientific and Technological Projects for the Returned Overseas Chinese Scholars, the Guizhou Province (Grant No. (2004)03), and the Top Talent’s Scientific Research Project of Organization Department of Guizhou Province     

The geometrical structure,electronic structure and magnetism of bimetallic Au<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>M<Subscript>2</Subscript> (<Emphasis Type="Italic">n</Emphasis>=1, 2; M=Y,Zr, Nb,Mo, Tc,Ru, Rh,Pd) clusters

The geometrical structure, stability, magnetism, and electronic structure of bimetallic clusters AuM₂ and Au₂M₂, where M are 4d transition metal elements, are investigated systematically by using the first-principles method based on density functional theory. The calculation results show that there is a large amount of low-energy isomers with the very similar structure. AuM₂ and Au₂M₂ clusters display dramatic magnetism. The magnetic moment of the 4d element is either enhanced or weakened with respect to the bulk value, which is largely dependent on the orbital exchange-splitting. Supported by the National Natural Science Foundation of China (Grant Nos. 10674015 and 10604035)     

Elastic stability and electronic structure of low energy tetragonal and monoclinic PdN2 and PtN2

This paper studies the elastic and electronic structure properties of two new low-energy structures of PdN2 and PtN2 by first-principles calculations.It finds that tetragonal and monoclinic structures are more stable than a pyrite one.The always positive eigenvalues of the elastic constant matrix confirm that both the tetragonal and monoclinic structures are elastically stable.The origin of the low bulk modulus of the two structures is discussed.The results of the calculated density of states show that both of the two low-energy structures are metallic.     

Electronic structures and magnetic properties in SmCo7-xMx

The electronic structures and magnetic properties of SmCo7 xMx (M=Ti, Si, Zr, Hf, Cu, B, Ag, Ga, Mn) compounds are investigated by using a spin-polarized MS-X.α method. The results show that the long-range ferromagnetic order is determined by a stronger 3d-5d interaction, rather than the traditional RKKY interaction, and the effects of doping element M on 3d-5d coupling are negligible in Sm-Co-based compounds. The nonmagnetic dopant Si atoms have a larger effect on the moments of 2e site although they preferably occupy the Co 3g sites, which results in the stronger uniaxial anisotropy of this compound. Analysis of the formation energies indicates that 5d-element doped compounds are more stable than other dopants, and furthermore, they have a higher Curie temperature above room temperature, which will be in favor of their potential application as high-temperature permanent magnets.     

A DFT/TD‐DFT study for the ground and excited states of peramine and some pyrrolopyrazinone compounds

Peramine, a heterocyclic natural molecule, reveals two main, different in nature, electronic absorption bands. Theoretical calculations at the TD‐B3LYP/6–311++G(d,p) level of theory show that the electronic excitations are connected predominantly with π → π^* and charge‐transfer (CT) transitions. Excitation of electrons from the pyrrolopyrazinone ring to the side chain plays a role in creating the CT transition. The character and energy of the first 30 singlet–singlet electronic transitions have also been investigated for the most stable conformation of peramine. Copyright © 2009 John Wiley & Sons, Ltd.     

Binding properties between ferroic oxides and metals

Using first principles calculations the binding characteristics of a metallic film covering a piezo-electric oxide is studied. The band structures and the charge densities of interfaces and single compounds are calculated. Comparing the overlaps of the densities of states and the differences in the charge densities, it is found that the interface stabilitydepends on the thickness of the metallic film. The bonding is shown to be a result of charge transfer.     

New mechanism for non-trivial intra-molecular vibrational dynamics

We investigate the time evolution process of one selected (initially prepared by optical pumping) vibrational molecular state S, coupled to all other intra-molecular vibrational states R of the same molecule, and also to its environment Q. Molecular states forming the first reservoir R are characterized by a discrete dense spectrum, whereas the environment reservoir Q states form a continuous spectrum. Assuming the equidistant reservoir R states we find the exact analytical solution of the quantum dynamic equations. S-Q and R-Q couplings yield to spontaneous decay of the S and R states, whereas S-R exchange leads to recurrence cycles and Loschmidt echo at frequencies of S-R transitions and double resonances at the interlevel reservoir R transitions. Due to these couplings the system S time evolution is not reduced to a simple exponential relaxation. We predict various regimes of the system S dynamics, ranging from exponential decay to irregular damped oscillations. Namely, we show that there are possible four dynamic regimes of the evolution: (i) independent of the environment Q exponential decay suppressing backward R - S transitions, (ii) Loschmidt echo regime, (iii) incoherent dynamics with multicomponent Loschmidt echo, when the system state is exchanged its energy with many states of the reservoir, (iv) cycle mixing regime, when long time system dynamics looks as a random-like. We suggest applications of our results for interpretation of femtosecond vibration spectra of large molecules and nano-systems.     

Mg合金晶粒细化机理的电子理论研究

采用递归法计算了α-Mg与α-Zr的结构能、原子结合能,Mg/Zr界面能与Mg/液态Mg界面能,Mg中Zr及Zr中Fe,Mn,Si等杂质原子相互作用能.计算发现α-Zr的结构能、原子结合能低于相应的α-Mg,且Mg/Zr界面能低于Mg/液态Mg界面能,从能量角度合理解释了Zr先于Mg从Mg熔体析出,并作为异质核心细化Mg晶粒的实验现象.原子相互作用能的计算结果显示,Zr在Mg中相互吸引形成团簇,并与杂质形成化合物,削弱晶粒细化效果. 关键词： 电子结构 晶粒细化 Mg合金     

Au和3d过渡金属元素混合团簇结构、电子结构和磁性的研究

采用基于密度泛函理论的第一性原理方法系统研究了Au与3d过渡元素构成的混合小团簇的结构、稳定性、电子结构及磁性,得到了Au与3d过渡元素构成的混合小团簇的稳定结构.计算结果表明,Au与3d元素可形成大量的低能异构体,特别是有些异构体在结构上极相近,这不同于共价或离子键类型的团簇.与纯过渡金属团簇类似,这类团簇也表现出复杂的磁性.过渡金属元素的磁矩相比体材料而言既有增强的、也有减弱的,与轨道的交换劈裂密切相关.对于基态构型,AuCr₂,Au₂Cr_{2关键词： 密度泛函理论 第一性原理方法 团簇 电子结构}