18983UC、UN、UH势函数及热力学性质的理论研究
关键词 UC, UN, UH, 势能函数, 密度泛函理论, 热力学性质
毕业设计说明书（毕业论文）外文摘要
Title Potential Function and Thermodynamic Property of UC UN，UH
Abstract
Potential energy scan for UC,UN,UH was performed by ab initio configuration interaction (CI) method, QCISD method, CCSD method and density functional theory methods at the PBE1 level in combination with the (ECP80MWB_AVQZ+2f) basis set for uranium and 6-311+G* for carbon, hydrogen, nitrogen. The dissociation energies of UC,UN,UH are -5.7960,-4.5077and-2.6999eV at the QCISD levels, respectively. The calculated energy was fitted to potential functions of Morse, Lennard-Jones, and Rydberg by using least square method. As to UC, The anharmonicity constant is 0.0047160.The anharmonic frequency is 780.27 cm–1 deduced from the PBE1 results. As to UN, The anharmonicity constant is 0.0049827.The anharmonic frequency is 812.65 cm–1 deduced from the PBE1 results. As to UH, The anharmonicity constant is 0.017300.The anharmonic frequency is 1449.8 cm–1 deduced from the QCISD results. Thermodynamic properties of entropy and heat capacity at different temperature were calculated using anharmonic frequency. They accords to DFT-UPBE1 results(for UC and UN)and QCISD results(for UH). The relationship between entropy and temperature was established.
Keywords UC,UN,UH, Potential function, Uranium oxide, Density functional theory, Thermodynamic property
目 次
1 引言3
2 基本原理5
2.1 计算化学5
2.2 从头计算方法5
2.3 密度泛函方法6
2.4 分子动力学模拟6
2.5 势函数7
3 计算方法8
4 计算结果和讨论10
4.1 势能10
4.2 热力学函数47
结论 50
致谢 51
参考文献 52
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1 引言
铀不仅是一种极其重要的战略核能材料，同时也作为核工程材料而被广泛使用。纯铀为银白色致密金属，有很强的化学活性，在大气中放置很短的时间就可以在它的表面上产生氧化[1]。尤其在高湿度、高温度的条件下, 容易受到环境介质中的水蒸气、氧气以及其它腐蚀性气体的侵蚀而变质。即便在超高真空的环境里，金属铀表面也会和残留的水或氧气发生反应，快速氧化从而形成氧化膜[2]，影响其核反应性能和材料力学性能。因而, 必须对铀材料实行表层保护或整体合金化才可以增强其抗腐蚀的效果, 进而预防其老化以及延长存储期。但无论是采用表面涂覆或是表面改性技术，都只能在一定程度上提高铀表面的抗腐蚀能力。只要金属铀与外界环境气氛接触，仍旧会发生化学腐蚀。