Pu2分子的结构与势能函数

用相对论有效原子实势(RECP)和密度泛函(B3LYP)方法对Pu2分子的结 构进行了优化,对较高多重性优化得到两个平衡结构,并用Murrell-Sorbie函数导出了基 态两种结构的势能函数和光谱数据。     

基态Li_n(n=2,3)结构与完全解析势能函数

使用Gaussian03程序包,采用全电子单双取代耦合簇(CCSD(full))方法,选择基组6-311+g(2df),对Li2分子的基态进行优化计算,采用十一参量Murrell-Sorbie函数,运用最小二乘法拟合得到Li2分子基态解析势能函数,给出与实验值符合很好的光谱常数;使用同样的方法和基组,对Li3分子的基态结构进行优化计算,得到Li3分子基态平衡结构.采用多体项展式法,利用Li3分子平衡结构C2v的几何参数、力常数和离解能,以及七个线性系数Ci(i=1,2,3,4,5,6,7)与两个非线性系数的函数关系,进行非线性优化拟合得到两个非线性系数,进而得到七个线性系数,得到Li3分子基态完全解析势能函数.势能面静态特征表明,该势能函数再现了Li3分子基态全部平衡结构特征.     

基态Bn(n=2, 3)结构与完全解析势能函数

使用Gaussian03程序包, 采用全电子单双取代耦合簇(CCSD(full))方法, 选择基组6-311+g(2df) , 对B2分子的基态进行优化计算, 采用十一参量Murrell-Sorbie函数, 运用最小二乘法拟合得到B2分子基态解析势能函数, 给出与实验值符合很好的光谱常数; 使用同样的方法和基组, 对B3分子的基态结构进行优化计算, 得到B3分子基态平衡结构. 采用多体项展式法, 利用B3分子平衡结构C2v的几何参数、力常数和离解能, 以及七个线性系数Ci(i=1, 2, 3, 4, 5, 6, 7)与两个非线性系数的函数关系, 进行非线性优化拟合得到两个非线性系数, 进而得到七个线性系数, 得到B3分子基态完全解析势能函数. 势能面静态特征表明, 该势能函数准确再现了B3分子基态全部平衡结构特征.     

基态Bn(n=2,3)结构与完全解析势能函数简

使用Gaussian03程序包,采用全电子单双取代耦合簇(CCSD(full))方法,选择基组6-311+g(2df),对B2分子的基态进行优化计算,采用十一参量Murrell-Sorbie函数,运用最小二乘法拟合得到B2分子基态解析势能函数,给出与实验值符合很好的光谱常数;使用同样的方法和基组,对B3分子的基态结构进行优化计算,得到B3分子基态平衡结构.采用多体项展式法,利用B3分子平衡结构C2v的几何参数、力常数和离解能,以及七个线性系数Ci(i=1,2,3,4,5,6,7)与两个非线性系数的函数关系,进行非线性优化拟合得到两个非线性系数,进而得到七个线性系数,得到B3分子基态完全解析势能函数.势能面静态特征表明,该势能函数准确再现了B3分子基态全部平衡结构特征.     

基态Lin(n=2, 3)结构与完全解析势能函数

使用Gaussian03程序包, 采用全电子单双取代耦合簇(CCSD(full))方法, 选择基组6-311+g(2df) , 对Li2分子的基态进行优化计算, 采用十一参量Murrell-Sorbie函数, 运用最小二乘法拟合得到Li2分子基态解析势能函数, 给出与实验值符合很好的光谱常数; 使用同样的方法和基组, 对Li3分子的基态结构进行优化计算, 得到Li3分子基态平衡结构. 采用多体项展式法, 利用Li3分子平衡结构C2v的几何参数、力常数和离解能, 以及七个线性系数Ci(i=1, 2, 3, 4, 5, 6, 7)与两个非线性系数的函数关系, 进行非线性优化拟合得到两个非线性系数, 进而得到七个线性系数, 得到Li3分子基态完全解析势能函数. 势能面静态特征表明, 该势能函数再现了Li3分子基态全部平衡结构特征.     

板翅式换热器传热、阻力多目标权衡优化

本文利用NSGA-Ⅱ算法对板翅式换热器中流体的传热和阻力分别引起的熵产数和(?)耗散数进行了多目标权衡优化。使传热和压降这两个相互矛盾的目标函数同时达到最优,并对帕累托前沿解域进行了LINMAP(多维偏好分析的线性规划)决策,最后对比了两种适值函数的优化结果。结果显示:换热器结构在11个自由度,并满足较小的熵产数或■耗散数的条件下,相比单一目标函数压降最大减少73.65%,成本最多节省1.61%;在相同换热效率下,煨耗散法优化得出的总成本比熵产法减少0.01%。     

用ab initio方法计算NaLi分子基态(X1∑+)的势能函数及光谱常数

运用原子分子群表示方法,首先确定NaLi分子的电子基态(X1∑ ).然后选用6-311 G(3df,2pd)基组优化计算得到NaLi分子基态(X1∑ )的平衡结构和离解能,采用电子相关QCISD(T)方法结合6-311 G(3df,2pd)基组对NaLi分子基态进行单点能扫描计算.最后用单点扫描计算值结合优化计算所得参数去拟合Murrell-Sorbie函数,得到了NaLi分子基态的势能函数.用该势能函数计算的光谱常数与实验结果符合得很好,表明拟合确定的势能函数能精确地描述基态NaLi分子的结构和性质.     

H2Se(X1A1)分子的解析势能函数

使用密度泛函B3LYP方法和 6-311++G**基组,在优化H2Se(X1A1)基态结构,确定其正确离解极限,计算所有两体项和三体项参数基础上,建立了H2Se(X1A1)的多体项展式解析势能函数。其中对处于激发态两体项HSe(A2∑+)的计算,则使用SAC-CI方法。H2Se(X1A1)的等值势能图准确地表现了其结构和势能面的特征。     

基态SiCO体系的分析势能函数

在从头计算的基础上,对基态SiCO体系的全势能表面用多体项展式方法进行优化,确定了分析势能函数.该势能函数准确再现了基态SiCO(X3Σ-)和SiOC( X3Σ-)的线性结构和能量,正确反映了SiCO(X3Σ-)和SiOC(X3Σ- )异构体的离解通道.     

H_2Se(~1A_1)分子的解析势能函数

使用密度泛函B3LYP方法和6-311++G~(**)基组,在优化H_2Se(~1A_1)基态结构,确定其正确离解极限,计算所有两体项和三体项参数基础上,建立了H_2Se(~1A_1)的多体项展式解析势能函数.其中对处于激发态两体项HSe(A~2∑~+)的计算,则使用对称匹配耦合簇一组态相关SAC—CI方法.H_2Se(~1A_1)的等值势能图准确地表现了其结构和势能面的特征.     

Pu(100)表面吸附CO2的密度泛函研究

采用广义梯度密度泛函理论的改进Perdew-Burke-Ernzerh方法结合周期性层晶模型,研究了CO₂分子在Pu（100）面上的吸附和解离.吸附能和几何构型的计算表明,CO₂以穴位C4O4构型吸附最为有利,吸附能为1.48 eV.布居分析和态密度分析表明,CO₂与Pu表面相互作用的本质主要是CO₂分子的杂化轨道2π_μ与Pu5f,Pu6d,Pu7s轨道通过强电子转移和弱重叠杂化的方式相互作用而生成了新的化学键.计算的CO₂→CO+O解离能垒为0.66 eV,解离吸附能为2.65 eV, 表明在一定热激活条件下CO₂分子倾向于发生解离性吸附.O₂,H₂,CO和CO₂在Pu （100）面吸附的比较分析表明,较低温度下的吸附强度顺序依次为O₂,CO,CO₂,H₂;较高温度下的吸附强度顺序依次为O₂,CO₂,CO,H₂. 关键词： 密度泛函理论 Pu （100） 2')" href="#">CO₂ 吸附和解离     

PuH2分子电子结构的DVM研究

关于钚的氢化物的分子结构和分子光谱公开解密的资料与数据甚少.基于密度泛函理论的全数值自洽场计算方法——离散变分方法(DVM)，数值解相对论的Dirac方程，在自由的钚原子和氢原子波函数的数值基及原子能级基础上计算了全电子的PuH2分子电子结构.得到PuH2分子基态最佳参数为键长Pu—H=0208617nm，键角θ°(H—H)=115.011°，轨道总能量为-19838.6630 a.u.，费米能级EF=-12.571eV. 比较了冻芯与非冻芯全电子计算结果.     

CO在Pu(100)表面吸附的研究

采用密度泛函理论(DFT)研究了CO分子在Pu (100)面上的吸附. 计算结果表明：CO在Pu (100)表面的C端吸附比O端吸附更为有利，属于强化学吸附. CO吸附态的稳定性为穴位倾斜>穴位垂直>桥位>顶位. CO分子与表面Pu原子的相互作用主要源于CO分子的杂化轨道和Pu原子的杂化轨道的贡献. 穴位倾斜吸附的CO分子的离解能垒较小(0.280eV)，表明在较低温度下，CO分子在Pu (100)表面会发生离解吸附，离解的C，O原子将占据能量最低的穴位.     

CO在Pu(100)表面吸附的研究

采用密度泛函理论(DFT)研究了CO分子在Pu (100)面上的吸附. 计算结果表明：CO在Pu (100)表面的C端吸附比O端吸附更为有利,属于强化学吸附. CO吸附态的稳定性为穴位倾斜>穴位垂直>桥位>顶位. CO分子与表面Pu原子的相互作用主要源于CO分子的杂化轨道和Pu原子的杂化轨道的贡献. 穴位倾斜吸附的CO分子的离解能垒较小(0.280eV),表明在较低温度下,CO分子在Pu (100)表面会发生离解吸附,离解的C,O原子将占据能量最低的穴位. 关键词： 密度泛函理论 Pu (100) CO 分子和离解吸附     

Incommensurate/commensurate charge-density-wave states as a source for plutonium metal behavior

Physical property behavior of plutonium (Pu) metal phases is like that of an incommensurate charge-density wave (ICDW) system where the CDW influenced distortion modulates the crystal. As incommensurates, the different Pu phases may have to be considered as superspace group structures where there is a one-dimensional modulation of the basic three-dimensional lattice. Certain Pu phases may then be classified into as many as three Bravais classes when considered in (3 + 1) dimensional space. The possible variants in Bravais class, crystals setting and bottom lines, as well as allowable differences in the number of atoms per unit cell, should permit incommensurate materials, as well as Pu phases, to appear in different variants of the basic space group structure on heating and cooling cycles. One should not expect the lower temperature phases, e.g., Pu, to return to their original distorted or modulated structures at constant rate cooling, after being distorted or modulated by CDWs in their higher temperature space group structures. This can explain the hysteresis in phase transitions noted with Pu metal and with incommensurate materials in general.

Chiral symmetry appears to be inherent to the incommensurability of a quasi-one dimensional system. All but one of the reported space group structures for Pu phases have at least a one-dimensional twofold screw axis with a center of symmetry, i.e., they show chiral symmetry. A theory suggests that chiral symmetry must permit the contraction in one or more dimensions noted with most incommensurate materials, as well as with Pu phases.

It is suggested that there is another ICDW Pu phase (αI) below ～ 60 K, and that the γ-Pu phase (Fddd) must be a composite structure. Other Pu phases appear to be composite structures also. There is evidence for a new phase, or phase mixture, which appears reproducibly between the δ and γ phases only on a cooling cycle. It is infered that this is a reappearance of the δ' phase.

Published dilatometry, internal friction and relative shear modulus results appear to confirm both incommensurate and commensurate CDW states in Pu metal phases. It is suggested that CDWs may be playing a role in f-bonding in Pu metal and that CDWs and valence fluctuations may be manifestations of the same electronic behavior.     

Radiolytic formation of plutonium (VII)

Abstract

Radiolytic oxidation of Pu(VI) to Pu(VII) in 1M NaOH solution has been investigated in presence of K₂S₂O₈. The radiolytic yield of Pu(VII), G[Pu(VTI)], has been found to depend both on the concentrations of Pu(VI) and K₂ S₂O₈., The maximum value of G [Pu(VII)] =4.0 has been obtained in solution containing 5.1 × 10^?4 M Pu(VI) and 7. 0 × 10^?2 M K₂S₂O₈.     

Photofission of 238Pu, 240Pu, and 242Pu in the energy range 5–10 MeV

The cross sections for the photofission of plutonium isotopes ²³⁸Pu, ²⁴⁰Pu, and ²⁴²Pu in the energy range 5–10 MeV have been measured by using a beam of bremsstrahlung photons from the microtron installed at the Institute of Physics and Power Engineering (Obninsk). The energy regions below the fission barrier and above 6 MeV have been scanned with pitches of 0.05 and 0.1 MeV, respectively. In deriving the absolute cross section for ²³⁸Pu photofission, ²³⁸U photofission has been employed as a reference reaction. In measurements involving ²⁴⁰Pu and ²⁴²Pu nuclei, the neptunium isotope ²³⁷Np, which is characterized by a more regular dependence of the photofission cross section on excitation energy than ²³⁸U, has been chosen for the first time as a reference nucleus. The measured cross sections as functions of energy show resonance structures in the vicinity of the fission threshold that are consistent with those previously observed in the energy dependences of fissilities for corresponding direct reactions. The partial-wave cross sections for the J ^π K = 1^?0, 1^?1, and 2⁺0 photofission channels have been determined as functions of energy. At energies below some 5.5 MeV, the total cross section for photofission of each plutonium isotope being studied receives a significant contribution from quadrupole interaction. Within the one-dimensional model of a two-humped fission barrier, the parameters of the barriers for ²³⁸Pu, ²⁴⁰Pu, and ²⁴²Pu have been extracted from data and have then been compared with estimates based on previous measurements.     

Pu2+2 分子离子的结构与势能函数

使用密度泛函B3LYP方法对Pu2+2分子离子进行了理论研究,结果表明,Pu2+2分子离子是亚稳定结构,基态电子状态为 13Σg,势能函数可以用Z-W函数来表征,并首次计算获得基态分子离子的力常数和光谱数据.     

High Pressure Theoretical Studies of Actinide Dioxides

Actinide dioxides (ThO 2 , UO 2 , Pu 2 etc.) compounds have the CaF 2 -type structure at ambient pressure and temperature. Under high pressure, they exist in the PbCl 2 -type structure, belonging to space group Pnma [1]. We have studied crystal structures under high pressure in actinide dioxides by means of first-principles self-consistent total-energy calculations with the non-local Perdew, Burke and Ernzerhof (PBE) exchange correlation using the full-potential linear-muffin-tin-orbital (FPLMTO) method. The atomic equilibrium volume, bulk modulus and transition pressure for actinide dioxides were calculated, covering the full pressure range for which the mentioned experiments have been done [2].     

A density functional study of plutonium dioxide

The electronic and geometric structures of bulk PuO₂ and its (110) surface have been studied using a periodic model within the generalized gradient approximation (GGA) of density functional theory (DFT). The sixty core electrons of the Pu atom have been represented by a relativistic effective core potential and scalar relativistic effects have been incorporated on the valence orbitals. For bulk PuO₂, we predict an equilibrium lattice constant of 10.10 a.u. and a cohesive energy of 17.28 eV, in good agreement with experimental data. For the (110) surface, upon relaxation, the distance between the top layer and the next layer is found to decrease by 0.12 ?, i.e. 5.3% of the corresponding interlayer distance in the bulk. The distance between the two oxygen atoms on the top layer is found to increase by 0.15 ?, i.e. 5.6% of the corresponding bulk value. The small surface relaxation energy of 0.268 eV per unit cell indicates the fair stability of this surface. The effective charges on Pu and O atoms show that the chemical bonding in this system is not purely ionic. Together with the metallic feature of the density of states (DOS) on the surface, the effective charge distribution provides some basis for understanding surface reactivity and corresponding support for catalysis. Received 16 June 2000