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2.
张秀荣  吴礼清  康张李  唐会帅 《物理学报》2011,60(5):53601-053601
采用密度泛函理论(DFT)中的B3LYP方法,在Lanl2dz基组水平上对(OsnN)0,±(n=1—6)团簇的各种可能构型进行了几何参数全优化,得到了它们的基态构型;并对基态构型的平均结合能(Eb) 、二阶能量差分(Δ2En) 、解离能(Ed)和能隙(Eg)进行了理论研 关键词nN0')" href="#">OsnN0 (n=1—6)团簇')" href="#">±(n=1—6)团簇 几何结构 稳定性 密度泛函理论  相似文献   

3.
The formation of cationic clusters in the laser ablation of CdS targets has been investigated as a function of wavelength and fluence by mass spectrometric analysis of the plume. Ablation was carried out at the laser wavelengths of 1064, 532, 355, and 266 nm in order to scan the interaction regimes below and above the energy band gap of the material. In all cases, the mass spectra showed stoichiometric Cd n S n + and nonstoichiometric Cd n S n−1+, Cd n S n+1+, and Cd n S n+2+ clusters up to 4900 amu. Cluster size distributions were well represented by a log-normal function, although larger relative abundance for clusters with n=13, 16, 19, 34 was observed (magic numbers). The laser threshold fluence for cluster observation was strongly dependent on wavelength, ranging from around 16 mJ/cm2 at 266 nm to more than 300 mJ/cm2 at 532 and 1064 nm. According to the behavior of the detected species as a function of fluence, two distinct families were identified: the “light” family containing S2+ and Cd+ and the “heavy” clusterized family grouping Cd2+ and Cd n S m +. In terms of fluence, it has been determined that the best ratio for clusterization is achieved close to the threshold of appearance of clusters at all wavelengths. At 1064, 532, and 355 nm, the production of “heavy” cations as a function of fluence showed a maximum, indicating the participation of competitive effects, whereas saturation is observed at 266 nm. In terms of relative production, the contribution of the “heavy” family to the total cation signal was significantly lower for 266 nm than for the longer wavelengths. Irradiation at 355 nm in the fluence region of 200 mJ/cm2 has been identified as the optimum for the generation of large clusters in CdS.  相似文献   

4.
张秀荣  康张李  郭文录 《中国物理 B》2011,20(10):103601-103601
WnC0,± (n=1-6) clusters are investigated by using the density functional theory (DFT) at the B3LYP/LANL2DZ level. We find that the neutral, anionic and cationic ground state structures are similar within the same size, and constituted by substituting a C atom for one W atom in the structures of Wn+1 clusters. The natural bond orbital (NBO) charge analyses indicate that the direction of electron transfer is from the W atom to the 2p orbital of the C atom. In addition, the calculated infrared spectra of the WnC0,± (n=2-6) clusters manifest that the vibrational frequencies of neutral, anionic and cationic clusters are similar in a range of 80 cm-1-864 cm-1. The high frequency, strong peak modes are found to be an almost stretched deformation of the carbide atom. Finally, the polarizabilities of WnC0,± (n=1-6) clusters are also discussed.  相似文献   

5.
李兵  杨传路  齐凯天  张岩  盛勇 《物理学报》2009,58(5):3104-3111
使用密度泛函理论(DFT)的杂化密度泛函B3LYP方法在6-31G*基组水平上对SimCnm+n≤7)团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构. 并对最稳定结构的平均结合能(Eb),二阶能量差分(Δ2E)和能隙(Eg)等进行了理论研究. 结果表明,随着原子个数的增加,SiC二元团 关键词mCnm+n≤7)团簇')" href="#">SimCnm+n≤7)团簇 密度泛函理论 结构与性质  相似文献   

6.
It is shown that the simplest strong-interaction models (those that employ the Breit boundary condition and a delta-function potential) involving only three free parameters describe adequately the properties of the dt and d 3He systems in the vicinity of the 5He*(3/2+) and 5Li*(3/2+) resonances—that is, at energies in the regions E≲3E C and E≲2E C where E C is the corresponding Coulomb energy. For these systems, the complex values of the scattering length, of the effective range, and of the shape parameter are extracted from experimental data on the reaction cross section and proton polarization in scattering (in the case of the d 3He system). The astrophysical function is extrapolated to the low-energy region (0≤E<0.1E C), which is of importance for thermonuclear investigations, but which is hardly accessible to direct measurements. __________ Translated from Yadernaya Fizika, Vol. 66, No. 1, 2003, pp. 89–99. Original Russian Text Copyright ? 2003 by Kulik, Mur.  相似文献   

7.
An all-electron scalar relativistic calculation on Au n Pt (n = 1−12) clusters has been performed by using density functional theory with the generalized gradient approximation at PW91 level. Our results reveal that all the lowest energy geometries of Au n Pt  (n = 1−12) clusters may be generated by substituting Pt atom for one gold atom of the Au n+1 cluster at the highest coordinated site. Compared with corresponding pure Au n+1 cluster, the lowest energy geometries of Au n Pt clusters are distorted slightly and still keep the planar structures due to the strong scalar relativistic effect in small gold cluster. The Au-Pt bonds are stronger and most Au-Au bonds far from Pt atom are weaker than the corresponding Au-Au bonds in pure Au n+1 cluster. By substituting Pt atom for one gold atom of Au n+1 cluster at the highest coordinated site, the relatively stable and inactive odd-numbered Au n+1 cluster becomes the relatively unstable and reactive odd-numbered Au n Pt cluster, and the relatively unstable and reactive even-numbered Au n+1 cluster becomes the relatively stable and inactive even-numbered Au n Pt  cluster chemically and electronically. All the Au n Pt clusters prefer low spin multiplicity. The even-numbered Au n Pt clusters are found to exhibit zero magnetic moment and the odd-numbered Au n Pt clusters are found to possess magnetic moment with the value of 1 μ B. The odd-even alterations of magnetic moments and electronic configurations for Au n Pt clusters are very obvious and may be simply understood in terms of the electron pairing effect.  相似文献   

8.
冯胜奇  邱庆春 《物理学报》2011,60(5):57106-057106
依据量子理论与配位场理论,利用群论和对称性分析的方法探讨了C2+4分子在具有D4h对称性构型时,E×(b1g+b2g)系统的Jahn-Teller效应中的相关问题.研究了C2+4分子的电子态与声子态的对称性及其活跃声子态,讨论了系统声子间的耦合与CG系数,构建了E×(b1g+b2g 关键词: 2+4分子')" href="#">C2+4分子 对称性 能级分裂 Jahn-Teller畸变  相似文献   

9.
温俊青  夏涛  王俊斐 《物理学报》2014,63(2):23103-023103
采用密度泛函理论方法,在BPW91/LANL2DZ水平下详细研究了Pt n Al(n=1—8)团簇的几何结构、稳定性和电子性质.同时,分析了团簇的结构演化规律、平均结合能、二阶能量差分、能隙、磁性、Mulliken电荷和电极化率.结果表明:除Pt2Al外,所有Pt n Al(n=1—8)团簇的基态几何结构都可以用Al原子替换Pt n+1基态构型中的Pt原子得到,且Al原子位于较高的配位点上.二阶能量差分、能隙的分析结果表明,PtAl和Pt4Al团簇相对其他团簇具有较高的稳定性.Mulliken电荷分析表明,Al原子所带的电荷转移到Pt原子上,Al原子是电荷的捐赠者.磁性的分析说明,单个Al原子的加入对Pt n团簇的平均每原子磁矩随尺寸的变化趋势没有影响,但总体上降低了Pt n团簇的平均磁矩.极化率的研究表明,富Pt团簇的非线形光学效应强,容易被外场极化.  相似文献   

10.
The geometries, electronic and magnetic properties of AlnAsq (q = ?1, 0, +1; n = 1–16) clusters have been investigated systematically by using an unbiased CALYPSO structure searching method and density functional theory. The lowest energy structures show that the As atom prefers to occupy the peripheral position of Aln+1 clusters instead of the endohedral position. For cationic and neutral clusters, the structural transition from bilayer-like structure to cage-like structure is observed at cluster size n = 12, while it occurs at n = 13 for anionic clusters. The calculated detachment energies (DEs), ionisation potentials (IPs) and electronic affinities (EAs) are consistent with the available experimental and theoretical results for small clusters, indicating that the calculated lowest energy structures are reliable. Furthermore, the DE, EA and IP values for cluster size n ≥ 6 are successfully predicted. A stability analysis shows that Al5As and Al12As+ clusters have relatively large HOMO–LUMO energy gaps, corresponding to the magic numbers of 20 and 40 valence electrons, respectively.  相似文献   

11.
D P Ahalpara 《Pramana》1979,12(2):179-201
The low-lying collective bands of positive parity states in (fp) shell nuclei are described in the deformed Hartree-Fock method by projecting states of definite angular momenta from ‘the lowest energy intrinsic states in (sd)−1 (fp) n+1 configurations. The modified Kuo-Brown effective interaction for (fp) shell and modified surface delta interaction (MSDI) for a hole in (sd) shell with a particle in (fp) shell have been used. The collective bands of states are in general well reproduced by the effective interactions. The excitation energies of the band head states are however off by about one MeV. The calculated magnetic moments of the band headj=3/2+ states are in reasonable agreement with experiment. Using effective chargese p=1.33e ande n=0.64e we get fairly good agreement forE(2) transitions. The hinderedM(1) transition strengths are reproduced to the correct order however they are slightly higher compared to experiment.  相似文献   

12.
The velocity dependence for the ionization of H2O and D2O to form H2O+ and D2O+ in collisions with both 23S and 21S metastable helium atoms has been measured in a crossed molecular beam apparatus using a mechanical velocity-selector on the metastable beam. The cross-sections are found to be proportional to the —n power of the relative collision energy, with n ? 0.4 for both metastable atoms in both gases. The branching ratios H2O+/OH+ and D2O+/OD+ were both found to be 4.3 for both metastable helium atoms, and to be independent of the relative collision energy.  相似文献   

13.
We consider bond percolation on the Z d lattice. Let M n be the number of open clusters in B(n)=[−n,n] d . It is well known that E p M n /(2n+1) d converges to the free energy function κ(p) at the zero field. In this paper, we show that s2p(Mn)/(2n+1)d\sigma^{2}_{p}(M_{n})/(2n+1)^{d} converges to −p(1−p)κ′(p).  相似文献   

14.
The low-temperature dc mobility of the two-dimensional electron system localized above the surface of superfluid helium is determined by the slowest stage of the longitudinal momentum transfer to the bulk liquid, namely, by the interaction between the surface and volume excitations of liquid helium, which decreases rapidly with the temperature. Thus, the temperature dependence of the low-frequency mobility is μdc ≈ 8.4 × 10−11 n e T −20/3 cm4 K20/3/(V s), where n e is the surface electron density. The relation T 20/3 E−3 ≪ 2 × 10−7 between the pressing electric field (in kilovolts per centimeter) and temperature (in Kelvins) and the value ω ≲ 108 T 5 K−5 s−1 of the driving-field frequency have been obtained, at which the above effect can be observed. In particular, E ≃ 1 kV/cm corresponds to T ≲ 70 mK and ω/2π ≲ 30 Hz.  相似文献   

15.
The Hartree-Bogoliubov (HB) framework of calculations has been applied for calculating various nuclear structure quantities for 154–166Dy mass chains. In this framework, the intrinsic quadrupole moments, the low-lying yrast states (E 2+ and E 4+) and occupation numbers for various shell model orbits have been obtained. The calculated results indicate that the observed onset of deformation in going from 154Dy to 166Dy arises due to enhanced occupation of (h 11/2)π orbit, increased polarization of (d 5/2)π orbit and increase in the occupation of down-slopping ‘k’ components of (i 13/2)υ and (h 9/2)υ orbits.   相似文献   

16.
I V S Rathore  B P Singh 《Pramana》1979,12(3):243-250
Some of the low-lying states in many isotopes144Nd,148Sm,152Gd and156Gd show a similar typical behaviour. The first 2+ is regarded as a single quadrupole phonon state and 3 as a single octupole phonon state. The levels with the spins and parities 1, 5, 3, 4, etc. are considered due to the simultaneous excitation of quadrupole and octupole phonons. If this consideration is correct, then the transition fromJ to 2+ states must contain an appreciableE3 content. Theβ-γ-γ angular correlation coefficients for the cascade ofβ-rays ofE max 800 keV→γ-rays of 1489 keV→γ-rays of 696 keV are used to estimateE3 content inE1 transition in144Nd.  相似文献   

17.
The results obtained by studying the angular distributions of gamma rays with respect to the neutron-beam axis in the reaction 178Hf(n, n′γ) involving the deexcitation of the K π = 0+ rotational bands of 178Hf are presented.New information about themultipole-mixing parameter δ in gamma transitions from the levels of these bands is obtained. The K π = 04+ band is constructed anew. The relationship between the parameter δ for the (2+0 n −2+01) gamma transition and the energy gap Δ n = E lev(2+0 n ) − E lev(0+0 n ), on one hand, and the quasiparticle structure of the rotational band, on the other hand, is discussed for 178Hf on the basis of the quasiparticle-phonon model.  相似文献   

18.
The ground-state energy of neutral helium is estimated variationally with a trial wavefunction of the form ϕ≈e −γ(rA/a o)ne−γ(rB/a o)n. This model represents a modification of traditional textbook examinations of this problem via inclusion of the power “n” as a second nonlinear variational parameter in addition to the usual effective nuclear charge γ and leads to an upper-limit on the ground state energy of −2.86107 E h (E h =1 hartree) in comparison with the traditional (n=1) result of −2.84766 E h . This result represents a reduction of the percentage overestimate from the true ground-state energy (−2.90373 E h ) of from 1.93 to 1.47. In comparison with the maximum accuracy obtainable from an uncorrelated trial wavefunction, −2.86168 E h , the present trial wavefunction reduces the percentage overestimate from 0.49 (n=1) to 0.021. The optimum values of (n, γ) are determined to be ≈(0.897, 1.825).  相似文献   

19.
This study is interested in the illustration of ab initio potential energy curves for Ba+Arn (n = 1–4) clusters. The electronic structures of these molecules are calculated using [Ba2+] and [Ar] non-empirical core pseudo-potentials complemented by the core polarisation operators for both atoms, which allow the consideration of core valence correlation effects. The structure and stabilities of Ba+Arn (n = 1–4) clusters are investigated. These molecules are treated as one-electron active system. Spectroscopic constants and vibrational energy levels have been derived from their potentials. The analysis of the geometric forms, basing on the potential energy curves and the spectroscopic constants, clearly shows the importance of rare gas induced dipole. We also show that the dipolar interactions can influence the coupling between atoms.  相似文献   

20.
冯选旗  冯雪红  姜振益 《物理学报》2010,59(11):7838-7844
通过采用7种密度泛函理论DFT方法对AlnC进行计算,所得结果与实验数据比较,选择了B3lyp方法和6-311G(d)基组对AlnC及AlnC+(n=1—8)团簇进行结构优化和频率分析,得到了AlnC及AlnC+基态以及亚稳态结构.当n从小到大变化时,这些团簇的结构从平面向立体过渡,平面构型以三角形为主,立体构型主要是三棱柱笼状结构;在这些团簇中的高对称性结构中,中性团簇和阳离子只能有其一是稳定构型;在所研究的团簇中,Al2C和Al5C团簇较为稳定.  相似文献   

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