Quantum mechanics discovers unusual crystal structure in calcium metal under high pressure
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A Swedish research team led by Professor Rajeev Ahuja and Prof. H.K. Mao from USA have used theoretical calculations to study high pressure behaviour of calcium and predicted a new type of incommensurate phase. This is the first time that such phase is discovered from theory. The findings are being published in this week's Net edition of Proceedings of the National Academy of Science, USA.
A Swedish research team led by Professor Rajeev Ahuja and Prof. H.K. Mao from USA have used theoretical calculations to study high pressure behaviour of calcium and predicted a new type of incommensurate phase. This is the first time that such phase is discovered from theory. The findings are being published in this week's Net edition of Proceedings of the National Academy of Science, USA.
Calcium is one of the element in whole periodic table which shows the highest Tc (superconducting temperature) under high pressure. At 160 GPa of pressure it reaches to a record value for an element of 25 K. In present paper in PNAS, we predict a incommensurate structure for Ca at high pressure from quantum mechanical calculations. The incommensurate phase in a pure element "must be the weirdest known atomic structure of a metal" (V. Heine, Nature 403, 836 (2000)).
Now, there is an increasing interest in understanding the complex behavior of simple elements under high pressure not only within the materials physics community, but also from the fundamental aspect of physics. So far, the incommensurate nature of the complex phase was resolved based on the analysis of X-ray diffraction pattern. It is not straightforward to apply quantum mechanical calculations to incommensurate phases because they are not periodic crystals. We show how one can use quantum mechanical technique to investigate an incommensurate structure, estimate the structure parameters and calculate the total energy accurately. Our findings may provide an explanation for the continuous rising of superconducting temperature in high-pressure calcium, and could lead us to the next breakthrough in superconducting materials.
The extensive numerical studies were performed at Uppsala University's Uppsala Multidisciplinary Center for Advanced Computational Science, UPPMAX.
Read the article on PNAS website.
For more information, please contact Dr. Sergiu Arapan, +46 (0)18-471 37 43; e-mail: sergiu.arapan@fysik.uu.se or Professor Rajeev Ahuja, phone: +46 (0)18-471 36 26; cell phone: +46 (0)70-425 09 35; e-mail: Rajeev.Ahuja@fysik.uu.se