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Phonon Dispersion Analysis as an Indispensable Tool for Correct Predictions of Solid State Polymorphism

Dominik Kurzydłowski 1Tomasz Jaroń 1Wojciech Grochala 1,2

1. Warsaw University, Faculty of Chemistry, Pasteura 1, Warszawa 02-093, Poland
2. Warsaw University, Interdisciplinary Centre for Matematical and Computational Modeling (ICM UW), Pawinskiego 5,building D,floor 5, Warszawa 02-106, Poland


Geometry optimization based on ab initio electronic structure calculations is a valuable tool for predicting structures of novel compounds in the solid state. But even the most precise optimization scheme can lead to a structure which is not a genuine minimum on the potential energy surface. That is the case for elusive bulk AuF for which three types of structures were proposed previously [1]. Our DFT (GGA/PBE) calculations of the phonon spectra revealed the presence of imaginary modes for all these polymorphs [2]. Distortion of the parent structures along the normal modes of imaginary phonons, and subsequent geometry reoptimization has led us to new polymorphs of AuF, free of imaginary lattice vibrations. Phonon - guided optimizations for a handful of possible polymorphs of XeAuF have yielded inter alia a quasi-molecular polymorph (derived from a well known InOBr structure) surpassing its predecessor in enthalpy by almost 0.4 eV [3]. These findings enabled us to propose viable high pressure (p > 10 000 atm) synthetic routes for both compounds [2,3].

To further highlight the usefulness of phonon dispersion analysis we have conducted calculations of the lattice dynamics of solid compressed silane, SiH4. The earlier theoretical studies have failed to correctly predict its crystal structure [4,5] (determined recently by x-ray diffraction [6]).

[1] T. Söhnel, H. Hermann and P. Schwerdtfeger, J. Phys. Chem. B 109 (2005) 526.

[2] D. Kurzydłowski, W. Grochala, Chem. Commun. 9 (2008) 1073.

[3] D. Kurzydłowski, W. Grochala, Z. Anorg. Allg. Chem. 634 (2008) 1082.

[4] J. Feng, W. Grochala, T. Jaroń R. Hoffmann, A. Bergara, N. W. Ashcroft, Phys. Rev. Lett. 96 (2006) 017006.

[5] C. J. Pickard, R. J. Needs, Phys. Rev. Lett. 97 (2006) 045504.

[6] O. Degtyareva, M. Martínez Canales, A. Bergara, X. J. Chen, Y. Song, V. V. Struzhkin, H. Mao, R. J. Hemley Phys. Rev. B 76 (2007) 064123.


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Presentation: Poster at E-MRS Fall Meeting 2008, Symposium J, by Dominik Kurzydłowski
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-12 13:56
Revised:   2009-06-07 00:48