Document Detail

Hybrid functional study rationalizes the simple cubic phase of calcium at high pressures.
MedLine Citation:
PMID:  23163378     Owner:  NLM     Status:  In-Data-Review    
Simple cubic (SC) phase has been long experimentally determined as the high-pressure phase III of elemental calcium (Ca) since 1984. However, recent density functional calculations within semi-local approximation showed that this SC phase is structurally unstable by exhibiting severely imaginary phonons, and is energetically unstable with respect to a theoretical body-centered tetragonal I4(1)∕amd structure over the pressure range of phase III. These calculations generated extensive debates on the validity of SC phase. Here we have re-examined the SC structure by performing more precise density functional calculations within hybrid functionals of Heyd-Scuseria-Erhzerhof and PBE0. Our calculations were able to rationalize fundamentally the phase stability of SC structure over all other known phases by evidence of its actual energetic stability above 33 GPa and its intrinsically dynamical stability without showing any imaginary phonons in the entire pressure range studied. We further established that the long-thought theoretical I4(1)∕amd structure remains stable in a narrow pressure range before entering SC phase and is actually the structure of experimental Ca-III(') synthesized recently at low temperature 14 K as supported by the excellent agreement between our simulated x-ray diffraction patterns and the experimental data. Our results shed strong light on the crucial role played by the precise electron exchange energy in a proper description of the potential energy of Ca.
Hanyu Liu; Wenwen Cui; Yanming Ma
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  The Journal of chemical physics     Volume:  137     ISSN:  1089-7690     ISO Abbreviation:  J Chem Phys     Publication Date:  2012 Nov 
Date Detail:
Created Date:  2012-11-20     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0375360     Medline TA:  J Chem Phys     Country:  United States    
Other Details:
Languages:  eng     Pagination:  184502     Citation Subset:  IM    
State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China.
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