金属电子关联函数的实空间变分计算

本文求解了在相关基函数理论框架下得到的实空间关联函数的积分方程,得到了金属铝(r_s=2.07)和铯(r_s=5.65)的关联函数,关联能和多体波函数。改进了其它多体理论,本文得到的关联函数是恒正的,并且满足归一化条件。 关键词：     

金属氢高温超导电性

本文利用晶体的平均电子半径r_s、离子质量M和声速v_j等较少参量表示Z价金属的有效声子谱α²F(ω)、电声子耦合常数λ和谱面积λ/2〈ω〉,并用Dynes的T_c公式,求得了金属氢、铅和铌的超导临界温度。计算表明,在零压下金属氢的λ=2.55,T_c=162K。 关键词：     

(Z)-1-溴-2-(对氯苯基)-1,2-双(对甲氧苯基)-乙烯晶体结构

题目化合物(C₂₂H₁₈O₂ClBr)为单斜晶系,空间群为(P2₁)/n,晶胞参数a=19.502(10)?,b=9.118(5)?,c=11.233(6)?;β=88.18(1)°。结构由MULTAN-80确定。首先在E图上确定了溴原子位置,由加权傅里叶综合定出了其余26个非氢原子坐标。原子坐标按各向同性和各向异性温度因子各修正两轮后,计算差值电子密度图,从差值图上找出了全部氢原子。氢原子坐标按各向同性和非氢原子按各 关键词：     

双金属团簇Cu12Fe吸附CO和H2的理论研究

基于第一性原理密度泛函理论(DFT)方法研究了Cu₁₂Fe团簇的结构稳定性、热力学稳定性和反应活性.计算得出正二十面体Fe原子核心团簇Ih-core比正二十面体Fe原子壳层团簇Ih-shell的热力学稳定性更强.通过分析吸附能讨论了CO和H₂在Ih-core团簇上的吸附构型.计算结果表明,Ih-core团簇以顶角Corner位吸附CO时吸附能最大,吸附模型最稳定,H₂吸附过程中发生了解离,两个氢原子均形成表面Facet位吸附构型.最后,通过分析前线轨道得到吸附过程的轨道信息.     

电场作用下S修饰C24N24从CO2/N2混合气体中选择性吸附CO2的第一性原理计算

在燃烧后气体中选择性捕获CO₂,对减缓因CO₂浓度过高引发的环境问题具有十分重要的意义.本文采用第一性原理计算的方法,研究了外加电场作用下S修饰C₂₄N₂₄富勒烯(S@C₂₄N₂₄)对CO₂的选择性吸附性能.首先研究了S@C₂₄N₂₄的结构和性质,发现其具有良好的稳定性.其次,研究了无电场时S@C₂₄N₂₄对CO₂的吸附行为,发现其吸附为弱的物理吸附.另外,进一步研究了外加电场作用下S@C₂₄N₂₄对CO₂的吸附行为.结果表明,结合距离(CO₂与S)和CO₂的键角(O=C=O)随电场的增大而减小;当电场增加到0.018 a.u.时,物理吸附转变为化学吸附.关闭电场时,化学吸附又转化为物理吸附.此外,即使在相同的电场条件...     

H2O在Pt(100)表面的预吸附态与高迁移性能

本文采用ASED-MO方法,计算了H₂O分子在Pt(100)面上不同吸附取向、不同吸附位置时的结合能,以及表面扩散激活能和扩散系数.计算结果表明,H₂0分子必须通过氢原子朝向衬底的预吸附态.才能进人氧原子朝向衬底的垂直顶位化学吸附状态.当H₂O分子处于上述预吸附态时,势能面极为平坦,扩散系数大,迁移性高. 关键词：     

Au(110)表面结构和氧原子吸附的第一性原理研究

用密度泛函理论(DFT)研究了金属Au(110)表面结构以及氧原子的吸附状态.计算得到Au(110)-(1×2)缺列再构表面原子的弛豫分别是-15.0%(Δd₁₂/d₀)和-1.1%(Δd₂₃/d₀),表面能为52.7 meV/²,功函数Φ=5.00 eV;Au(110)-(1×3)缺列再构表面的Δd_{1 关键词： 缺列再构Au(110)表面 STM图像 氧原子吸附}     

金属表面的相关波函数理论(Ⅱ)——实际计算

在文献[1]给出的理论框架的基础上,由具有Feenberg-Jastrow关联因子的相关波函数,计算了“jellium”模型下简单金属的表面能和电子密度分布。表面电子密度分布由求解Cha-kravarty-Woo方程而得到。由于库伦关联的长程性,在表面能和CW积分方程中都出现一系列的发散项,本文证明了所有发散项严格互相抵消。本文求得的表面能在整个实际金属的电子密度范围内(r_s=2—6)与实验值大致符合。 关键词：     

对氯苯甲酰哌啶晶体结构

对氯苯甲酸哌啶(C₁₂NOH₁₄Cl)的晶体属正交晶系,空间群为P2₁ 2₁ 2₁,晶胞参数为a=11.490(6)?,b=10.462(5)?,c=9.928(5)?,晶胞内分子数z=4。用PW-1100四圆衍射仪收集强度数据,Patterson法确定了氯原子的位置,Fourier综合获得了全部非氢原子位置,用全矩阵最小二乘法修正结构,最终的偏离因子R=0.094。差值Fourier综合确定了氢原子的位置。利用氯原子的反常散射效应确定了绝对构型。 关键词：     

Aun(n=2,3,4)团簇与乙醇分子相互作用的第一性原理研究

利用密度泛函理论研究了Au_n(n=2,3,4)团簇与乙醇分子的吸附机理.研究结果表明:Au_n(n=2,3,4)团簇分别能够吸附1到n个乙醇分子,生成Au_n-(C₂H₆O)_1-n配合物;Au₄团簇吸附乙醇分子有多种构型,通过分析吸附能和Mulliken电荷分布,确定了4个乙醇分子的吸附顺序及相应的稳定构型;Au_n(n=3,4)团簇在吸附最后一个乙醇分子时改变了前面Au—O成键的作用模式,而是选择Au—H成键;作为吸附主体的金团簇和被吸附的乙醇分子在吸附前后构型变化都很少,它们之间的吸附作用为弱相互作用. 关键词： 金团簇 乙醇分子 密度泛函理论     

Electronic structure of adsorbed alkali atoms for comparison with UPS data

We have generalised our earlier work calculating the induced density of states in alkali chemisorption to include the valence np level in addition to the s level. This allows the theory to take account of the possibility of sp hybridization. Hybridization is said to be weak is the sp level separation ΔE_sP exceeds twice the width of the s or p_z resonance. In the converse case hybridization is strong and the induced density of states no longer reflects distinguishable s and p_z resonances. We argue that ΔE_sP for the chemisorbed alkali exceeds considerably that for the free alkali atom. In the case of Na on r_s = 2 jellium (considered typical of the smaller alkali on r_s = 2?3 substrates) hybridization is strong for the atomic value of ΔE_sp but weak when a somewhat larger value is taken, making the conclusions a little indefinite. For Cs on Cu(111), we find a clear situation of weak hybridization with the atomic ΔE_sP and a fortiori with a more realistic value. There should thus be a well defined 6s resonance in this system. Our estimate of the width of the 6s resonance is in good agreement with photoemission data.     

On-top density in the nonlinear metallic screening and its implication on the exchange-correlation energy functional

In comparison with the accurate data on the on-top electron density n(0) in the proton-embedded electron gas with the density parameter r_s in the range 1?12 obtained by diffusion Monte Carlo (DMC) simulations, we have successfully constructed an alternative form of the exchange-correlation energy functional in the density functional theory by imposing the constraint due to the cusp theorem on the well-known Perdew–Burke–Ernzerhof (PBE) functional. Although PBE does not, our functional, referred to as the cusp-corrected PBE (ccPBE), reproduces the DMC data on n(0) in the entire range of r_s.     

On the ground state energy of a two-dimensional electron fluid

A new theory of the ground state energy of a two-dimensional electron fluid is presented. It is shown that the ring diagram contribution changes its analytical behavior atr _s =2^1/2, wherer _s is the usual density parameter defined by r_S = 1/a ₀( n)^1/2,a ₀ being the Bohr radius andn is the electron density. For smallr _s , a high density series is obtained in agreement with the previous calculation. For larger _s , a hitherto unknown low density series is obtained. In the low density region, the first order exchange energy is completely cancelled out by a term from the ring contribution so that the ground state energy decreases in proportion tor _s ^–2/3 , followed byr _s ^/–4/3 and higher order terms. The energy is found to be minimum atr _s=1.4757, the minimum value being –0.481915 Rydbergs.     

Andreev-Lifshitz supersolid revisited for a few electrons on a square lattice. I

In 1969, Andreev and Lifshitz have conjectured the existence of a supersolid phase taking place at zero temperature between the quantum liquid and the solid. In this and a succeeding paper, we re-visit this issue for a few polarized electrons (spinless fermions) interacting via a U/r Coulomb repulsion on a two dimensional L×L square lattice with periodic boundary conditions and nearest neighbor hopping t. This paper is restricted to the magic number of particles N = 4 for which a square Wigner molecule is formed when U increases and to the size L = 6 suitable for exact numerical diagonalizations. When the Coulomb energy to kinetic energy ratio r _s = UL/(2t ) reaches a value r _s ^F ≈ 10, there is a level crossing between ground states of different momenta. Above r _s ^F, the mesoscopic crystallization proceeds through an intermediate regime ( r _s ^F < r _s < r _s ^W ≈ 28) where unpaired fermions with a reduced Fermi energy co-exist with a strongly paired, nearly solid assembly. We suggest that this is the mesoscopic trace of the supersolid proposed by Andreev and Lifshitz. When a random substrate is included, the level crossing at r _s ^F is avoided and gives rise to a lower threshold r _s ^F(W) < r _s ^F where two usual approximations break down: the Wigner surmise for the distribution of the first energy excitation and the Hartree-Fock approximation for the ground state. Received 21 June 2002 Published online 14 February 2003 RID="a" ID="a"e-mail: jpichard@cea.fr     

On the ground state energy of a two-dimensional electron fluid

A new theory of the ground state energy of a two-dimensional electron fluid is presented. It is shown that the ring diagram contribution changes its analytical behavior atr _s =2^1/2, wherer _s is the usual density parameter defined by r_S = 1/a ₀(π n)^1/2,a ₀ being the Bohr radius andn is the electron density. For smallr _s , a high density series is obtained in agreement with the previous calculation. For larger _s , a hitherto unknown low density series is obtained. In the low density region, the first order exchange energy is completely cancelled out by a term from the ring contribution so that the ground state energy decreases in proportion tor _s ^?2/3 , followed byr _s ^/?4/3 and higher order terms. The energy is found to be minimum atr _s=1.4757, the minimum value being ?0.481915 Rydbergs.     

Effective spin susceptibility, electron mass and Landé factor in two-dimensional (2D) Si inversion layers

We have studied the silicon (Si) band-structure, electron–electron and electron-ionized donor interaction effects on our accurate and approximate results (AcR and ApR) for renormalized effective spin susceptibitity (RESS), electron mass (EEM), Landé factor and spin polarization in the impure 2D Si (electron system), showing that:(i) our ApR, being strongly deviated from our AcR, reproduces approximately all the data obtained recently by Pudalov et al. (Phys. Rev. Lett. 88 (2002) 196404) [in particular, RESS =4.7 at the critical value of Wigner–Seitz radius r_s: r_s=r_c≈8.5 at which occur the “apparent” metal–insulator transition (MIT)] and can also be compared with other ApRs found in the recent literature,(ii) both the RESS and EEM produce physical singularities at the same critical value: r_s=r_c11.05661 (weakly disordered samples) at which occurs the “true” MIT; the existence of such two “apparent and true” critical values in this impure system agrees with a recent discussion by Abrahams et al. (Rev. Mod. Phys. 73 (2001) 251), and(iii) at r_s=r_c=8.5, at which occurs the “apparent” MIT, our AcR for effective spin polarization and the corresponding result, obtained using a disordered Hubbard model and a determinant quantum Monte Carlo method by Denteneer and Scalettar (Phys. Rev. Lett. 90 (2003) 246401), both give the same result: ξ_eff.=ξ_c0.31 at B0.4 T, which is found to be lower than the critical parallel magnetic field for full spin polarization, B_c=1.29 T, supporting thus the existence of such an “apparent” MIT.     

THE EFFECT OF LATTICE VIBRATION ON THE MAGNETISM IN METALLIC HYDROGEN

In this note, a new approach is adopted to the magnetism in metallic hydrogen, i.e., based on the Kim theory and Stoner model the electron-phonon interaction is introduced into the itinerant electron mag-netism theory. A calculation of spontaneous magnetization of metallic hydrogen at T=0 K shows that in spite of no change in the para- to ferro-magnetism value, r_sc of W-S radius r_s, the spontaneous magnetic moment of electron in ferromagnetic state, where r_s>>r_sc, is considerably reduced by lattice vibrations.     

Dynamics of the crystallized one-component plasma

The dynamics and energy of the crystallized one-component plasma (OCP) is evaluated using the self-consistent-phonon (SCP) theory of lattice dynamics. Melting of the crystal is also examined. The OCP crystal is harmonic for particle rms vibrational amplitudes as large as 25% of the interparticle spacing. This is due to the soft (r^?1) core of the Coulomb potential. Anharmonic effects are, however, entirely responsible for the eventual mechanical instability, identified here with melting, of the crystal at large enough rms amplitudes. This takes place at r_s = 180 at T = 0 K for the most sophisticated SCP theory. In the classical limit, this SCP theory predicts the crystal to be more stable than does the “exact” Monte Carlo study of melting by Pollock and Hansen. This suggests that including further anharmonic terms in the SCP theory leads to melting at even larger r_s at T = 0 K. However, comparison of crystal and fluid energies by Ceperley, Hansen, and Mazighi suggest melting in the range r_s = 65 to 135. Near melting the anharmonic contributions shift the phonon frequencies by a factor of 2 and the phonon lifetimes become very short.     

A model for viscosity coefficients of gases with potentials differing in form

A recent theory of non-conformal interactions has been very succesful in providing effective spherical potentials for the pressure of more than 40 real gases and many of their binary mixtures. Here, this theory is applied to deal with low-density viscosity coefficients. In its simplest form, the approximate non-conformal (ANC) theory introduces, besides the usual corresponding states parameters-energy ? and distance r_m-a softness parameter s to account for the form of a particular potential function. We investigate the effects of the potential form on the temperature behaviour of the viscosisty coefficient η. It is shown that the softer potentials, with wider attractive wells, have larger viscosities and an explicit expression for η (T, ?, r_m, s) is obtained. The ANC potentials are tested in their capacity to reproduce the temperature dependence of η for the heavier noble gases (Ar, Kr and Xe), diatomics (H₂, N₂, O₂ and CI₂) and a dozen small polyatomics. It is found that the ANC model η (T, ?, r_m, s), with only three substance-dependent parameters, reproduces experimental 7 data within their estimated error.