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Exotic behavior and crystal structures of calcium under pressure

AutorOganov, Artem R.; Ma, Yanming; Errea, Ion; Bergara, Aitor
Palabras claveEvolutionary algorithms
High pressure
Structure prediction
Density functional theory
Fecha de publicaciónabr-2010
EditorNational Academy of Sciences (U.S.)
CitaciónProceedings of the National Academy of Sciences 107(17): 7646–7651 (2010)
ResumenExperimental 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 β-tin (I41/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. A.B. gratefully acknowledges financial support from the European Commission 6th framework Network of Excellence NANOQUANTA (NMP4-CT-2004-500198). I.E. thanks the Basque Department of Education and Research for financial help.
Descripción6 páginas, 7 figuras.-- et al.
Versión del editorhttp://dx.doi.org/10.1073/pnas.0910335107
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