First-principles pressure-temperature phase diagrams in metals
- Lawrence Livermore National Laboratory, University of California, Livermore, California 94550 (United States)
Using interatomic potentials derived from first-principles generalized pseudopotential theory, finite--temperature phase transitions in both simple and transition metals can be studied through a combination of analytic statistical methods and molecular-dynamics simulation. In the prototype simple metal Mg, where volume and pair forces adequately describe the energetics, a complete and accurate phase diagram has thereby been obtained to 60 GPa. A rapidly temperature-dependent hcp-bcc phase line is predicted which ends in a triple point on the melting curve near 4 GPa. In central transition metals such as Mo or Fe, on the other hand, the energetics are complicated by [ital d]-state interactions which give rise to both many-body angular forces and enhanced electron-thermal contributions. We have made a detailed study of these phenomena and their impact on melting in the prototype case of Mo and a full melting curve to 2 Mbar has been obtained. In the case of Fe, we are examining the high-pressure phase diagram and the question of whether or not there exists a high-pressure, high-temperature solid bcc phase, as has been speculated. To date, we have shown that the bcc structure is both thermodynamically and mechanically [ital unstable] at high pressure and zero temperature, with a large and increasing bcc-hcp energy difference under compression. [copyright] 1994 American Institute of Physics
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 7183690
- Report Number(s):
- CONF-921145-; CODEN: APCPCS
- Journal Information:
- AIP Conference Proceedings (American Institute of Physics); (United States), Vol. 309:1; Conference: Production and neutralization of negative ions and beams, Upton, NY (United States), 9-13 Nov 1992; ISSN 0094-243X
- Country of Publication:
- United States
- Language:
- English
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