HgTe小团簇几何结构与电子性质的第一性原理研究

本文基于密度泛函理论的第一性原理方法,在广义梯度近似(GGA)下,计算了团簇 (HgTe)n(n＝1～8)的基态几何结构、最高占据轨道和最低未占据轨道的能隙、结合能等.比较了团簇(HgTe)n和(CdSe)n基态结构,能隙与结合能随尺寸变化关系的差异等.     

应用第一性原理对CdSe和HgTe团簇结构和电子性质的第一性原理研究

应用密度泛函理论的第一性原理方法(DMOL3程序),在广义梯度近似(GGA)下,对(HgTe)n和(Cdse)n团簇的基态结构、能隙、结合能等进行了计算,并对两种团簇的能隙、结合能随尺寸的变化关系进行了比较.     

MgS和MgSe带隙的GW近似修正（英文）

应用基于密度泛函理论下的局域密度近似(DFT-LDA)方法研究了岩石矿结构的MgS和MgSe的晶体结构和能带结构.本文得到稳定结构的晶格常数与已知实验数据相吻合,MgS和MgSe都是间接带隙半导体且带隙值分别为2.74 eV和1.70 eV.尽管本文利用LDA计算的带隙值与之前的理论值很接近,但是局域密度近似常常低估带隙值.因此应用准粒子GW(G是格林函数,W是库伦屏蔽相互作用)近似对MgS和MgSe的带隙值进行了修正,其结果分别为4.15 eV和2.74 eV.GW近似的结果应该是合适的值.     

强交换场中无隙超导电性的Eliashberg方程研究

本文研究强交换场中线性化的Eliashberg能隙方程。采用一个叠代方法考虑了能隙函数φ(ω)对±ω的不对称性。在叠代的最低阶给出了近似的解。所得的结果表明:对中等耦合强度以上(λ≥0.5)的电声子系统,能隙函数的不对称效应会显著影响临界交换场的数值。 关键词：     

电子间关联作用对过渡金属氧化物磁矩的影响

采用局域自旋密度近似(LSDA)下的线性丸盒轨道原子球近似(LMTO-ASA)能带方法,通过计入在位库仑作用U的方法来考虑电子间的多体关联作用(简写成LSDA+U方法),同时还进一步使用了平均占有数近似.用这种方法对过渡金属氧化物NiO和MnO进行了计算,结果表明如果仅着眼于考虑磁性则可以采用本文中的近似方法,但当涉及能隙问题时,则必须考虑不同m态的不同占有情况. 关键词：     

α-BeH_2电子结构与光学性质的第一性原理研究

基于密度泛函理论,采用赝势平面波方法研究了α-BeH2的结构、电子和光学性质.基态下,α-BeH2晶格常数a和体积弹性模量B0计算值与实验值及其它理论值一致.根据能带理论研究了α-BeH2基态下的能带结构、总态密度(DOS)和分波态密度(PDOS).经过分析发现α-BeH2为直接能隙半导体材料,能隙为5.44eV,与文献相比,本文计算的结果偏低,这主要是利用第一性原理中的局域密度近似(LAD)或广义梯度近似(GGA)交换关联能函数计算材料的带隙宽度或者磁耦合的理论结果均会偏低.通过对基态α-BeH2的Mulliken电荷分布和集居数的分析发现:α-BeH2属于离子键和共价键所形成的混合键化合物;α-BeH2的电荷总数分别来源于H1s轨道,Be2s和2p轨道.同时本文还分析研究了α-BeH2的光学介电函数、吸收系数、复折射率、反射系数和能量损失等光学性质.     

MC20F20(M=Li,Na,Be和Mg)几何结构和电子性质的密度泛函计算研究

采用密度泛函理论(density functional theory, DFT)中的广义梯度近似(generalized gradient approximation, GGA)对MC20F20(M=Li,Na,Be和Mg)的几何结构和电子性质进行了计算研究.几何结构研发现:随着内掺原子序数的增加,金属原子M对C20F20中的C-C键的影响越来越大,而对C-F键的影响甚微.掺杂能计算表明:MC20F20的掺杂能均为负值,需要在一定的实验条件下才能被合成.内掺碱金属和碱土金属分别产生了两类截然不同的能隙和磁性.其中,内掺碱金属的能隙非常小,且带有1μB的净磁矩,表现出磁性;而内掺碱土金属的能隙比C60的能隙还大,净自旋为0,表现出非磁性.     

Ge( SiO2)n团簇结构和电子性质的密度泛函理论研究

采用密度泛函理论中的广义梯度近似(GGA)对Ge(SiO2)n(n=1～7)团簇的几何构型进行优化,并对能量、频率和电子性质进行了计算.结果表明,Ge(SiO2)n的最低能量结构是在(SiO2)n端位O原子以及近邻端位O原子的Si原子上吸附一个Ge原子优化得到;随着锗原子数的增加,增加的锗原子易与原来的锗原子形成锗团簇.掺杂锗原子后团簇的能隙比(SiO2)n团簇的能隙小,当多个Ge原子掺杂到(SiO2)3团簇时,其能隙随着Ge原子个数的增加出现了振荡,Gem(SiO2)3的能隙从可见光区到近红外光区变化.二阶能量差分、分裂能表明Ge(SiO2)2和Ge(SiO2)5团簇是稳定的.     

中小尺寸CdS和CdTe团簇结构与电子性质的第一性原理研究

基于密度泛函理论(DFT)的第一性原理方法(DMOL3程序),在广义梯度近似(GGA)下,计算了中小尺寸II~VI族(CdS)n和(CdTe)n团簇的基态结构、最高占据轨道(HOMO)和最低未占据轨道(LUMO)的能隙、结合能等,比较了(CdS)n和(CdTe)n两种团簇的基态结构,能隙与结合能随尺寸变化关系的差异等.     

第一性原理对Co_mAg_n(m+n=13)团簇的几何结构和性质的研究

本文利用第一性原理的广义梯度近似(GGA)对Co_mAg_n(m+n=13)团簇进行了研究,在几何优化计算的基础上,分析了Co_mAg_n(m+n=13)团簇的束缚能、能隙和磁性.结果表明:Co_mAg_n(m+n=13)团簇束缚能的二阶能量差分在m=6,8,10,12时出现峰值,说明Co6Ag7,Co8Ag5,Co10Ag3,Co12Ag1团簇相对稳定;能隙的研究说明Co6Ag7团簇较其他团簇有较高的化学稳定性;在Co_mAg_n(m+n=13)团簇中增加Co原子数目有助于磁性的增强.     

Evidence for a kaon-bound state K(-)pp produced in K(-) absorption reactions at rest

We have searched for a deeply bound kaonic state by using the FINUDA spectrometer installed at the e(+)e(-) collider DAPhiNE. Almost monochromatic K(-)'s produced through the decay of phi(1020) mesons are used to observe K(-) absorption reactions stopped on very thin nuclear targets. Taking this unique advantage, we have succeeded to detect a kaon-bound state K(-)pp through its two-body decay into a Lambda hyperon and a proton. The binding energy and the decay width are determined from the invariant-mass distribution as 115(+6)(-5)(stat)(+3)(-4)(syst) MeV and 67(+14)(-11)(stat)(+2)(-3)(syst) MeV, respectively.     

Direct evidence for neutrino flavor transformation from neutral-current interactions in the Sudbury Neutrino Observatory

Observations of neutral-current nu interactions on deuterium in the Sudbury Neutrino Observatory are reported. Using the neutral current (NC), elastic scattering, and charged current reactions and assuming the standard 8B shape, the nu(e) component of the 8B solar flux is phis(e) = 1.76(+0.05)(-0.05)(stat)(+0.09)(-0.09)(syst) x 10(6) cm(-2) s(-1) for a kinetic energy threshold of 5 MeV. The non-nu(e) component is phi(mu)(tau) = 3.41(+0.45)(-0.45)(stat)(+0.48)(-0.45)(syst) x 10(6) cm(-2) s(-1), 5.3sigma greater than zero, providing strong evidence for solar nu(e) flavor transformation. The total flux measured with the NC reaction is phi(NC) = 5.09(+0.44)(-0.43)(stat)(+0.46)(-0.43)(syst) x 10(6) cm(-2) s(-1), consistent with solar models.     

Bonding in Cu,Ag, and Au clusters: relativistic effects,trends, and surprises

Electronic structure and bonding in anionic coinage metal clusters are investigated via density-functional calculations, focusing on an extensive set of isomers of Cu(-)(7), Ag(-)(7), and Au(-)(7). While the ground states of Cu(-)(7) and Ag(-)(7) are three dimensional (3D), that of Au(-)(7) is planar, separated from the optimal 3D isomer by 0.5 eV. The simulated thermally weighted photoabsorption spectrum of Au(-)(7) is dominated by planar structures, and it agrees well with the measured one. The propensity of Au(-)(N) clusters to favor planar structures (with N as large as 13) is correlated with strong hybridization of the atomic 5d and 6s orbitals due to relativistic effects.     

Evaluation of Expansion Coefficients from Optimal Fitting Parameters for the Analysis of Spectra of Diatomic Molecules and an Application to LiH

To evaluate individual expansion coefficients composing fitting parameters of the Born-Oppenheimer corrections to Dunham's coefficients Y(ij) that have been given analytically with the Delta(B) and Delta(omega) formalism, we examined the consistency of analytic expressions for those corrections with Watson's assertion of the experimental inseparability of nonadiabatic corrections Q(a, b)(r) for a molecule AB. Derived analytic expressions in terms of optimal fitting parameters for the corrections are essential to evaluate individual expansion coefficients. These expressions also reveal redundancies between empirical correction parameters Delta(ij). A method of evaluating nonadiabatic vibrational corrections Q(a, b)(r) and adiabatic corrections S(a, b)(r) separately consistent with Watson's assertion of inseparability is presented and is applied to an analysis of spectral data of LiH. Functions Q(a, b) and S(a, b) for LiH are thus successfully evaluated; S(H, Li)(r) values agree well with those predicted simply by wobble-stretch theory. Experimental values for optimal fitting parameters r(H)(1q) and r(H)(2q) are nearly equal to those of r(Li)(1q) and r(Li)(2q), respectively, in agreement with a theoretical relation r(a)(iq)=r(b)(iq). Copyright 2001 Academic Press.     

η-production on the proton via electromagnetic and hadronic probes

The reactions π~-p→ηn and γp→ηp are investigated within a dynamical coupled-channels model of meson production reactions in the nucleon resonance region. The meson-baryon channels included are πN, ηN, π△, σN, and ρN. The direct η-photoproduction process is studied within a formalism based on a chiral constituent quark model approach, complemented with a one-gluon-exchange mechanism, to take into account the breakdown of the SU(6) O(3) symmetry. In the models search, the following known nucleon resonances are embodied: S_(11)(1535), S_(11)(1650), P_(11)(1440), P_(11)(1710), P_(13)(1720), D_(13)(1520), D_(13)(1700), D_(15)(1675), and F_(15)(1680). Data for the π~-p→ηn reaction from threshold up to a total center-of-mass energy of W ≈ 2 GeV are satisfactorily reproduced. For the photoproduction channel, two additional higher mass known resonances, P_(13)(1900) and F_(15)(2000), are also considered. However, reproducing the data for γp→ηp requires, within our approach, two new nucleon resonances, for which we extract mass and width.     

Measurements of the D(sJ) resonance properties

We report measurements of the properties of the D(+)(sJ)(2317) and D(+)(sJ)(2457) resonances produced in continuum e(+)e(-) annihilation near sqrt[s]=10.6 GeV. The analysis is based on an 86.9 fb(-1) data sample collected with the Belle detector at KEKB. We determine the masses to be M(D(+)(sJ)(2317))=2317.2+/-0.5(stat)+/-0.9(syst) MeV/c(2) and M(D(+)(sJ)(2457))=2456.5+/-1.3(stat)+/-1.3(syst) MeV/c(2). We observe the radiative decay mode D(+)(sJ)(2457)-->D(+)(s)gamma and the dipion decay mode D(+)(sJ)(2457)-->D(+)(s)pi(+)pi(-) and determine their branching fractions. No corresponding decays are observed for the D(sJ)(2317) state. These results are consistent with the spin-parity assignments of 0(+) for the D(sJ)(2317) and 1(+) for the D(sJ)(2457).     

Experimental constraints on the spin and parity of the Lambdac(2880)+

We report the results of several studies of the Lambda(c)(+)pi(+)pi(-)X final state in continuum e(+)e(-) annihilation data collected by the Belle detector. An analysis of angular distributions in Lambda(c)(2880)(+)-->Sigma(c)(2455)(0,++)pi(+,-) decays strongly favors a Lambda(c)(2880)(+) spin assignment of 5/2 over 3/2 or 1/2. We find evidence for Lambda(c)(2880)(+)-->Sigma(c)(2520)(0,++)pi(+,-) decay and measure the ratio of Lambda(c)(2880)(+) partial widths Gamma(Sigma(c)(2520)pi)/Gamma(Sigma(c)(2455)pi)=0.225+/-0.062+/-0.025. This value favors the Lambda(c)(2880)(+) spin-parity assignment of 5/2(+) over 5/2(-). We also report the first observation of Lambda(c)(2940)(+)-->Sigma(c)(2455)(0,++)pi(+,-) decay and measure Lambda(c)(2880)(+) and Lambda(c)(2940)(+) mass and width parameters. These studies are based on a 553 fb(-1) data sample collected at or near the Upsilon(4S) resonance at the KEKB collider.     

Measurement of the ZZ production cross section and limits on anomalous neutral triple gauge couplings in proton-proton collisions at sqrt[s] = 7 TeV with the ATLAS detector

A measurement of the ZZ production cross section in proton-proton collisions at sqrt[s] = 7 TeV using data corresponding to an integrated luminosity of 1.02 fb(-1) recorded by the ATLAS experiment at the LHC is presented. Twelve events containing two Z boson candidates decaying to electrons and/or muons are observed, with an expected background of 0.3 ± 0.3(stat)(-0.3)(+0.4)(syst) events. The cross section measured in a phase-space region with good detector acceptance and for dilepton masses within the range 66 to 116 GeV is σ(ZZ → ?+ ?- ?+ ?-)(fid) = 19.4(-5.2)(+6.3)(stat)(-0.7)(+0.9)(syst) ± 0.7(lumi) fb. The resulting total cross section for on-shell ZZ production, σ(ZZ)(tot) = 8.5(-2.3)(+2.7)(stat)(-0.3)(+0.4)(syst) ± 0.3(lumi) pb, is consistent with the standard model expectation of 6.5(-0.2)(+0.3) pb calculated at the next-to-leading order in QCD. Limits on anomalous neutral triple gauge boson couplings are derived.     

First observation of the P-wave spin-singlet bottomonium states hb(1P) and hb(2P)

We report the first observations of the spin-singlet bottomonium states h(b)(1P) and h(b)(2P). The states are produced in the reaction e(+)e(-)→h(b)(nP)π(+)π(-) using a 121.4 fb(-1) data sample collected at energies near the Υ(5S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. We determine M[h(b)(1P)]=(9898.2(-1.0-1.1)(+1.1+1.0)) MeV/c(2) and M[h(b)(2P)]=(10,259.8±0.6(-1.0)(+1.4)) MeV/c(2), which correspond to P-wave hyperfine splittings ΔM(HF)=(+1.7±1.5) and (+0.5(-1.2)(+1.6)) MeV/c(2), respectively. The significances of the h(b)(1P) and h(b)(2P) are 5.5σ and 11.2σ, respectively. We find that the production of the h(b)(1P) and h(b)(2P) is not suppressed relative to the production of the Υ(1S), Υ(2S), and Υ(3S).     

Residual symmetries for neutrino mixing with a large θ13 and nearly maximal δD

The residual Z(2)(s)(k) and Z(2)(s)(k) symmetries induce a direct and unique phenomenological relation with θx (≡ θ13) expressed in terms of the other two mixing angles θs(≡ θ12) and θa(≡ θ23) and the Dirac CP phase δD. Z(2)(s)(k) predicts a θx probability distribution centered around 3°-6° with an uncertainty of 2°-4°, while those from Z(2)(s)(k) are approximately a factor of 2 larger. Either result fits the T2K, MINOS, and Double Chooz measurements. Alternately, a prediction for the Dirac CP phase δD results in a peak at ± 74° (± 106°) for Z(2)(s)(k) or ± 123° (± 57°) for Z(2)(s)(k) which is consistent with the latest global fit. We also give a distribution for the leptonic Jarlskog invariant Jν which can provide further tests from measurements at T2K and NOνA.