Abstract: 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.
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Lee, T.; Baskes, M.I.; Lawson, A.C.; Chen, S.P.; Valone, S.M. Atomistic Modeling of the Negative Thermal Expansion in δ- Plutonium Based on the Two-State Description. Materials 2012, 5, 1040-1054.
Lee T, Baskes MI, Lawson AC, Chen SP, Valone SM. Atomistic Modeling of the Negative Thermal Expansion in δ- Plutonium Based on the Two-State Description. Materials. 2012; 5(6):1040-1054.
Lee, Tongsik; Baskes, Michael I.; Lawson, A. C.; Chen, Shao Ping; Valone, Steven M. 2012. "Atomistic Modeling of the Negative Thermal Expansion in δ- Plutonium Based on the Two-State Description." Materials 5, no. 6: 1040-1054.