First-principles study of paraelectric and ferroelectric CsH2PO4 including dispersion forces: Stability and related vibrational, dielectric, and elastic properties

Van Troeye, Benoît;van Setten, Michiel;Giantomassi, Matteo;Torrent, Marc;Gonze, Xavier;et.al.
(2017) Physical review. B, Condensed matter and materials physics — Vol. 95, n° 2, p. 24112 (2017)

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Abstract
Using density functional theory (DFT) and density functional perturbation theory (DFPT), we investigate the stability and response functions of CsH2PO4, a ferroelectric material at low temperature. This material cannot be described properly by the usual (semi)local approximations within DFT. The long-range e−-e− correlation needs to be properly taken into account, using, for instance, Grimme’s DFT-D methods, as investigated in this work. We find that DFT-D3(BJ) performs the best for the members of the dihydrogenated alkali phosphate family (KH2PO4, RbH2PO4, CsH2PO4), leading to experimental lattice parameters reproduced with an average deviation of 0.5%. With these DFT-D methods, the structural, dielectric, vibrational, and mechanical properties of CsH2PO4 are globally in excellent agreement with the available experiments (<2% MAPE for Raman-active phonons). Our study suggests the possible existence of a new low-temperature phase of CsH2PO4, not yet reported experimentally. Finally, we report the implementation of DFT-D contributions to elastic constants within DFPT.
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Van Troeye, B., van Setten, M., Giantomassi, M., Torrent, M., Rignanese, G.-M., & Gonze, X. (2017). First-principles study of paraelectric and ferroelectric CsH2PO4 including dispersion forces: Stability and related vibrational, dielectric, and elastic properties. Physical review. B, Condensed matter and materials physics, 95(2), 24112. https://doi.org/10.1103/PhysRevB.95.024112 (Original work published 2017)