An ab initio molecular orbital study of the nuclear volume effects in uranium isotope fractionations.
An ab initio molecular orbital study of the nuclear volume effects in uranium isotope fractionations.
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DOI：
10.1063/1.2992616
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发表时间：
2008-10
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影响因子：
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通讯作者：
M. Abe;Tatsuya Suzuki;Y. Fujii;M. Hada;K. Hirao
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文献类型：
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作者：
M. Abe;Tatsuya Suzuki;Y. Fujii;M. Hada;K. Hirao
本文通过一系列从头算分子轨道计算，讨论了U(3+)-U(4+)和U(4+)-UO(2) (2+)体系中铀同位素分馏的核体积依赖性。同位素分馏系数（与ε相同）中的核体积相关项（与ln K(nv)相同）是根据系统中涉及的同位素异构体的能量平衡计算的。我们使用 Dirac-Coulomb Hartree-Fock (DCHF) 方法和高斯型有限核模型。我们采用三种类型的一般收缩高斯基组来检查基组依赖性。在 U(3+)-U(4+) 体系中，除了具有最小双 zeta 基组的值外，铀的 ln K(nv) 当前值与费米型有限核模型的数值原子多构型 DCHF 方法获得的 ln K(nv) 先前值非常一致。本计算合理地重现了 U(3+)-U(4+) 系统中 epsilon 的实验值以及 U(4+)-UO(2) (2+) 系统中 ln K(nv) 的值，这些值是通过对实验 epsilon 值进行温度相关拟合而凭经验获得的。例如，在 U(4+)-UO(2) (2+) 体系中，使用最大基组时，(235)U-(238)U 同位素对的当前从头计算 ln K(nv) 值为 0.002 09，而实验值为 0.002 24。本文还表明，核体积对 U-O 键长和两个力常数的影响可以忽略不计。 UO(2) (2+)。因此，同位素分馏系数的分子振动项主要取决于核质量而不是核体积。
This paper discusses the nuclear volume dependence of uranium isotope fractionations in the U(3+)-U(4+) and U(4+)-UO(2) (2+) systems by reference to a series of ab initio molecular orbital calculations. Nuclear volume-dependent terms ( identical withln K(nv)) in isotope fractionation coefficients ( identical withepsilon) are calculated from the energetic balance of the isotopomers involved in the systems. We used the Dirac-Coulomb Hartree-Fock (DCHF) method with the Gaussian-type finite-nucleus model. We employed three types of generally contracted Gaussian basis sets to check the basis set dependences. In the U(3+)-U(4+) system, the present values of ln K(nv) for uranium, other than those with the smallest double-zeta basis set, are in good agreement with previous values of ln K(nv) obtained from a numerical atomic multiconfigurational DCHF method with the Fermi-type finite-nucleus model. The present calculations reasonably reproduce the experimental value of epsilon in the U(3+)-U(4+) system, and the value of ln K(nv) in the U(4+)-UO(2) (2+) system, obtained empirically by temperature-dependent fitting of the experimental epsilon values. For instance, in the U(4+)-UO(2) (2+) system, the present ab initio ln K(nv) value for a (235)U-(238)U isotope pair is 0.002 09 using the largest basis set, while the experimental value is 0.002 24. This paper also shows that nuclear volume effects are negligibly small on the U-O bond length and two force constants of UO(2) (2+). Hence, the molecular vibrational terms of the isotope fractionation coefficients mainly depend on the nuclear mass rather than the nuclear volume.