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Peng J, Zhang S, Refson K, Dove MT. Unique features of the structural phase transition in acetylene showing simultaneous characteristics of reconstructive, displacive and order-disorder. Phys Chem Chem Phys 2023; 25:9909-9924. [PMID: 36946889 DOI: 10.1039/d3cp00400g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/18/2023]
Abstract
We have studied the two phases of the molecular crystal acetylene, C2H2, using calculations of the lattice dynamics by Density Functional Theory methods. together with the use of classical molecular dynamics (MD) simulation methods. The two phases share the same simple face-centred cubic lattice arrangement of the molecular centres of mass, but with different molecular orientations. We show that the higher-temperature phase has lower phonon frequencies and hence higher entropy, giving thermodynamic stability at higher temperature. The calculated lattice dynamics of this phase show instabilities associated with phonons involving pure rotations of the molecules. The MD results show large amplitudes of librational motion in this phase. The MD simulations also showed a potential phase transition to a structure of tetragonal symmetry. The picture that emerges is that the phase transition in acetylene is a very rare example of one that encompasses elements of three types of transition: displacive, order-disorder and reconstructive.
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Affiliation(s)
- Jie Peng
- College of Physics, Sichuan University, Chengdu, Sichuan 610065, China
| | - Sijie Zhang
- Guizhou University of Engineering Science, Xueyan Road, Bijie, Guizhou, 55170, China
- College of Physics, Sichuan University, Chengdu, Sichuan 610065, China
| | - Keith Refson
- ISIS Facility, Harwell Campus, Chilton, Didcot, OX11 0QX, UK
| | - Martin T Dove
- College of Computer Science, Sichuan University, Chengdu, Sichuan 610065, China.
- School of Mechanical Engineering, Dongguan University of Technology, 1st Daxue Road, Songshan Lake, Dongguan, Guangdong 523000, China
- School of Physical and Chemical Sciences, Queen Mary University of London, Mile End Road, London, E1 4NS, UK.
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Affiliation(s)
- Kimberly Shuler
- Department of Chemistry, Indiana UniversityPurdue University Indianapolis, 402 North Blackford Street, Indianapolis, Indiana 46202
| | - Clifford E. Dykstra
- Department of Chemistry, Indiana UniversityPurdue University Indianapolis, 402 North Blackford Street, Indianapolis, Indiana 46202
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