Two-dimensional crystals of classical particles are very peculiar in that melting may occur in two steps, in a continuous fashion, via an intermediate hexatic fluid phase exhibiting quasi-long-range orientational order. On the other hand, three-dimensional spheres repelling each other through a fast-decaying bounded potential of generalized-exponential shape (GEM4 potential) can undergo freezing into cluster crystals, allowing for more that one particle per lattice site. We hereby study the combined effect of low spatial dimensionality and extreme potential softness, by investigating the phase behavior of the two-dimensional (2D) GEM4 system. Using a combination of density-functional theory and numerical free-energy calculations, we show that the 2D GEM4 system displays one ordinary and several cluster triangular-crystal phases, and that only the ordinary crystal first melts into a hexatic phase. Upon heating, the difference between the various cluster crystals fades away, eventually leaving a single undifferentiated cluster phase with a pressure-modulated site occupancy.
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14 November 2014
Research Article|
November 12 2014
Hexatic phase and cluster crystals of two-dimensional GEM4 spheres
Santi Prestipino;
Santi Prestipino
a)
1Dipartimento di Fisica e di Scienze della Terra,
Università degli Studi di Messina
, Contrada Papardo, I-98166 Messina, Italy
2
CNR-IPCF
, Viale F. Stagno d’Alcontres 37, I-98158 Messina, Italy
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Franz Saija
Franz Saija
b)
2
CNR-IPCF
, Viale F. Stagno d’Alcontres 37, I-98158 Messina, Italy
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a)
Author to whom correspondence should be addressed. Electronic mail: sprestipino@unime.it
b)
Email: saija@ipcf.cnr.it
J. Chem. Phys. 141, 184502 (2014)
Article history
Received:
September 09 2014
Accepted:
October 29 2014
Citation
Santi Prestipino, Franz Saija; Hexatic phase and cluster crystals of two-dimensional GEM4 spheres. J. Chem. Phys. 14 November 2014; 141 (18): 184502. https://doi.org/10.1063/1.4901302
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