Lee Tongsik, Baskes Michael I, Lawson A C, Chen Shao Ping, Valone Steven M
Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
Jacobs School of Engineering, University of California, San Diego, La Jolla, CA 92093, USA.
Materials (Basel). 2012 Jun 7;5(6):1040-1054. doi: 10.3390/ma5061040.
The δ phase of plutonium with the fcc structure exhibits an unusual negative thermal expansion (NTE) over its narrow temperature range of stability, 593-736 K. An accurate description of the anomalous high-temperature volume effect of plutonium goes beyond the current capability of electronic-structure calculations. We propose an atomistic scheme to model the thermodynamic properties of δ-Pu based on the two-state model of Weiss for the Invar alloys, inspired by the simple free-energy analysis previously conducted by Lawson et al. The two-state mechanism is incorporated into the atomistic description of a many-body interacting system. Two modified embedded atom method potentials are employed to represent the binding energies of two competing electronic states in δ-Pu. We demonstrate how the NTE takes place in δ-Pu by means of Monte Carlo simulations implemented with the two-state mechanism.
具有面心立方结构的钚的δ相在其狭窄的稳定温度范围593 - 736 K内表现出异常的负热膨胀（NTE）。对钚异常高温体积效应的准确描述超出了当前电子结构计算的能力。受Lawson等人先前进行的简单自由能分析的启发，我们提出了一种基于因瓦合金的Weiss双态模型对δ - 钚的热力学性质进行建模的原子模型。双态机制被纳入多体相互作用系统的原子描述中。采用两种修正的嵌入原子方法势来表示δ - 钚中两种竞争电子态的结合能。我们通过采用双态机制进行的蒙特卡罗模拟展示了δ - 钚中NTE是如何发生的。
