Relative Stability of Calcium Chalcogenides from Ab initio Theory

The equations of state and phase stability of calcium chalcogenides, CaS, CaSe and CaTe are investigated via first principles theoretical calculations. We report results of the structural properties of these compounds in the B1(NaCl) and the B2(CsCl) phases, the theoretical transition pressure and the volumes compression ratio. For CaTe we investigate the possible existence of an intermediate phase between the B1 and the B2 structure.     

Ab initio interatomic potentials for low-energy He ion/atom scattering

Ab initio (density functional theory) binary interatomic potentials have been calculated for low-energy He projectile interactions with target atoms having atomic numbers (Z ₂) from 6 to 54 (C to Xe). The calculated potentials cover the energy range that is typical for low-energy ion He ion/atom-scattering spectroscopy (≤2–7 keV, depending on Z ₂). For constant R, the screening function exhibits Z ₂ oscillations that are indicative of the electronic stabilities of the corresponding quasi-molecules; screening function minima are observed for the quasi-molecules that are isoelectronic with the noble gases. The He–Z ₂ interatomic potentials calculated for target elements lighter than Rb are suitable for use in simulations of low-energy ion-scattering experiments. However, the potentials calculated for target atoms heavier than Kr do not offer any clear benefits over the existing empirical potentials. The solid-state potential shift applicable to scattering in metallic solids has been estimated as typically 0 to+10 eV, using a simple thermodynamic model that exploits the similarities between the valence states of an He–Z ₂ quasi-molecule and the corresponding united atom.     

Ab initio calculation of the 4He(e, e'd )d reaction

The two-body knock-out reaction ⁴He(e, e'd )d is calculated at various momentum transfers. The full four-nucleon dynamics is taken into account microscopically both in the initial and the final states. As NN interaction the central MT-I/III potential is used. The calculation shows a strong reduction of the coincidence cross-section due to the final-state interaction. Nonetheless, the theoretical results exhibit a considerable overestimation of the experimental cross-section at lower momentum transfer. Comparisons with other, less complete, calculations suggest that consideration of a more realistic ground state might not be sufficient for a good agreement with experiment, rather a more realistic final-state interaction could play an essential role.     

He+2团簇结构和解析势能函数的从头计算研究

采用从头计算的耦合簇方法CCSD(T)和He原子Dunning's相关调和基函数组对He+2团簇的结构参数、势能曲线进行计算.利用Murrell-Sorbie函数和最小二乘法拟合出了解析势能函数,并以此为基础计算出光谱常数.通过比较发现:分子结构和光谱常数计算结果均与实验值符合良好,优于文献报道的结果.说明本文所得势能函数解析表达式准确反映了分子中原子间相互作用,可用于更广泛的研究.     

Ab initio finite-temperature excitons

The coupling with the lattice vibrations is shown to drastically modify the state-of-the-art picture of the excitonic states based on a frozen-atom approximation. The zero-point vibrations renormalize the bare energies and optical strengths. Excitons acquire a nonradiative lifetime that decreases with increasing temperature. The optical brightness turns out to be strongly temperature-dependent such as to induce bright to dark (and vice versa) transitions. The finite-temperature experimental optical absorption spectra of bulk Si and hexagonal BN are successfully explained without using any external parameter.     

N-甲替甲酰胺-水的氢键团簇的从头计算研究

利用从头计算方法在MP2 / 6 31+G 和MP2 / 6 311++G(d ,p)水平上对N 甲替甲酰胺 (NMF) 水氢键团簇进行了研究 .计算给出了所有中性和离子化NMF H2 O团簇的优化结构、解离通道以及解离能 .对于N 甲替甲酰胺 ,顺式结构比反式结构具有更低的能量 .对于质子化的NMF ,质子倾向于连接在甲替甲酰胺的氧原子上 .计算结果表明 ,NMF的顺式和反式构型都可以与水分子形成线型的氢键结构 .尽管NMF反式结构比顺式结构能量高 ,但由于反式结构能与水分子形成双氢键 ,因此能更稳定的存在 .N 甲替甲酰胺 水团簇电离后 ,无论顺式和反式结构均有质子化产物生成 .     

Ab Initio Study of Electroweak Responses of 4He

In this contribution, we discuss the electroweak responses of ⁴He based on a full four-body calculation. The wave function of the ground state is obtained accurately using an explicitly correlated basis. Four-body final states are expressed in a superposition of many basis functions including configurations which have 3+1 and 2+1+1 cluster partitions of four-nucleon system explicitly. The continuum is properly treated by taking the two approaches: one is the complex scaling method and the other is the microscopic R-matrix method. The calculated photoabsorption cross sections agree up to the rest energy of a pion. The spin–dipole strength function is also presented and its relationship between the spectrum of ⁴He is discussed.     

Ab initio path-integral molecular dynamics

A path-integral molecular dynamics technique for strongly interacting atoms using ab initio potentials derived from density functional theory is implemented. This allows the efficient inclusion of nuclear quantum dispersion in ab initio simulations at finite temperatures. We present an application to the quantum cluster H ₅ ⁺ .     

Ab initio yield curve dynamics

We derive an equation of motion for interest-rate yield curves by applying a minimum Fisher information variational approach to the implied probability density. By construction, solutions to the equation of motion recover observed bond prices. More significantly, the form of the resulting equation explains the success of the Nelson–Siegel approach to fitting static yield curves and the empirically observed modal structure of yield curves. A practical numerical implementation of this equation of motion is found by using the Karhunen–Lòeve expansion and Galerkin's method to formulate a reduced-order model of yield curve dynamics.     

Ab initio studies on all-trans-polyene

Ab initio crystal orbital calculations have been performed on all-trans-polyene using a minimal STO-3G basis set. Several ground state properties such as the equilibrium structure, the most important force constants, the band structure and the density of states are reported. An alternant structure with $\text{r}{}_{\mathrm{<mtext>C=C</mtext>}}\text{= 1.327}\text{A}\text{?}$, $\text{r}{}_{\mathrm{<mtext>C-C</mtext>}}\text{= 1.477}\text{A}\text{?}$, $\text{?}\text{CCC}\text{= 124.2°}$ and $\text{r}{}_{\mathrm{<mtext>C-H</mtext>}}\text{= 1.085}\text{A}\text{?}$ was found to have the lowest energy.     

Ab initio investigation of uranium monochalcogenides

We present ab initio investigation of the electronic structure and magnetic properties of uranium monochal-cogenides: US, USe, UTe. The calculations were performed by using the recently developed LDA+U+SO method in which both Coulomb and spin-orbit interactions have been taken into account in rotationally invariant form. We discuss the problem of choice of the Coulomb interaction value. The calculated [111] easy axes agree with those experimentally observed. The electronic configuration 5f ³ was found for all uranium compounds under investigation.     

氘、氚代聚苯乙烯单体abinitio研究

用HF,MP2及BLYP从头算方法,在6—31G基组水平上,优化了聚苯乙烯单体基态的平衡几何构型.主要用BLYP6—31方法研究了氘、氚代聚苯乙烯单体(DPS,PST)的正则振动频率、红外光谱强度、C—D键键能,并对正则振动模式进行了简单分析,同时研究了DPS,PST单体中温度、压强与熵的关系. 关键词： 平衡几何构型 正则振动频率 红外光谱强度 键能     

Ab initio properties of gaseous helium

Recent ab initio calculations of the interaction potential of helium, and the effects of the new potentials on the calculated properties of helium gas (density and acoustic virials, viscosity, and thermal conductivity) are reviewed. To cite this article: J.B. Mehl, C. R. Physique 10 (2009).     

甲醛与甲酰胺相互作用的从头算研究

在MP2 /6 3 1G(d)和MP2 (FC) /6 3 11+ +G(d ,p)水平上 ,对H2 CO和HCONH2 以及设计的 3种构型H2 CO…HCONH2 复合物等进行几何全优化计算 ,经振动频率分析 ,确认它们为势能超曲面上的稳定驻点 .然后在MP2 /6 3 11+ +G(2df,3p)水平上进行单点能计算和基组重叠误差 (BSSE)校正以获得相互作用能 .并利用自然键轨道理论和分子中的原子理论探讨H2 CO和HCONH2 相互作用的本质 .分子间相互作用的能量分解分析显示 ,静电能在H2 CO…HCONH2 相互作用能中占主导地位     

Ab initio study of H and He migrations in β-phase Sc, Y, and Er hydrides

Ab initio calculations based on the density functional theory have been performed to investigate the migrations of hydrogen(H) and helium(He) atoms in β-phase scandium(Sc),yttrium(Y),and erbium(Er) hydrides with three different ratios of H to metal.The results show that the migration mechanisms of H and He atoms mainly depend on the crystal structures of hydrides,but their energy barriers are affected by the host-lattice in metal hydrides.The formation energies of octahedral-occupancy H(H oct) and tetrahedral vacancy(V tet) pairs are almost the same(about 1.2 eV).It is of interest to note that the migration barriers of H increase with increasing host-lattice atomic number.In addition,the results show that the favorable migration mechanism of He depends slightly on the V tet in the Sc hydride,but strongly on that in the Y and Er hydrides,which may account for different behaviours of initial He release from ScT2 and ErT2.