Accuracy of equation-of-state formulations

نویسندگان

  • RONALD E. COHEN
  • OGUZ GÜLSEREN
  • RUSSELL J. HEMLEY
چکیده

The accuracy of equation-of-state formulations is compared for theoretical total energies or experimental pressure-volume measurements for H2, Ne, Pt, and Ta. This spans the entire range of compression found for minerals and volatiles in the Earth. The Vinet equation is found to be most accurate. The origin of the behavior of different equation-of-state formulations is discussed. It is shown that subtle phase transitions can be detected by examining the residuals from an equation-ofstate fit. A change in the electronic structure of Ta is found at high pressures using this procedure, and a possible new transition in H2. and Wang (1998) for further discussion of thermal equations of state. To test equation-of-state formulations, it is important to study large compressions, because most common equations of state will work reasonably over small compression ranges. Thus we choose to study the very compressible materials, hydrogen and neon. We also consider tantalum and platinum, which are useful pressure standards. ISOTHERMAL OR STATIC EQUATIONS OF STATE The Birch equation of state (Birch 1978) is based on a series expansion of pressure P f K f f K f ( ) ( ) ' = + + − ( ) +     3 1 2 1 3 2 4 0 0 5 2 K (1) in terms of the Eulerian strain ƒ, where f V V =     − 

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تاریخ انتشار 1999