Monday, 11 February 2019

Relativity makes mercury liquid

The link between the theory of General Relativity and the orbit of the planet Mercury is pretty well-know.  What I learned recently is that it is a consequence of Special Relativity that the element mercury is liquid at room temperature.  

In a paper by Krista G. Steenbergen, Elke Pahl, and Peter Schwerdtfeger (J. Phys. Chem. Lett. 8, 1407 (2018)) the authors perform calculations of bulk mercury using both relativistic and non-relativistic quantum mechanics, and show that the use of relativity lowers the melting point of mercury by 160 K.  The relativistic calculations give a melting point close to nature (within 10K).  They are sophisticated quantum mechanical calculations in which bulk many-body effects are taken into account.  You can't simulate melting and freezing by considering the interaction of two or three atoms, but need at least tens of them to get a realistic picture of bulk matter.  That's not easy to calculate, and the authors have made a convincing case that they have done so, and that the dominant effect in causing mercury's unusually low melting point comes from relativity.

The picture below is from the paper, showing the result of a simulation with a disordered liquid phase on the left, becoming an ordered solid on the right.  

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