Exotic behavior and crystal structures of calcium under pressure.
Experimental studies established that calcium undergoes several counterintuitive transitions under pressure: fcc --> bcc --> simple cubic --> Ca-IV --> Ca-V, and becomes a good superconductor in the simple cubic and higher-pressure phases. Here, using ab initio evolutionary simulations, we explore the behavior of Ca under pressure and find a number of new phases. Our structural sequence differs from the traditional picture for Ca, but is similar to that for Sr. The beta-tin (I4(1)/amd) structure, rather than simple cubic, is predicted to be the theoretical ground state at 0 K and 33-71 GPa. This structure can be represented as a large distortion of the simple cubic structure, just as the higher-pressure phases stable between 71 and 134 GPa. The structure of Ca-V, stable above 134 GPa, is a complex host-guest structure. According to our calculations, the predicted phases are superconductors with Tc increasing under pressure and reaching approximately 20 K at 120 GPa, in good agreement with experiment.
Oganov
Artem R
AR
Department of Geosciences, New York Center for Computational Sciences, Stony Brook University, Stony Brook, NY 11794-2100, USA.
Ma
Yanming
Y
Xu
Ying
Y
Errea
Ion
I
Bergara
Aitor
A
Lyakhov
Andriy O
AO
D000465:Algorithms; D002118:Calcium / Q000737:chemistry*; D003198:Computer Simulation; D004553:Electric Conductivity; D008956:Models, Chemical; D008958:Models, Molecular; D011312:Pressure; D014961:X-Ray Diffraction
D002118:Calcium
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