Structure and energetics of a ferroelectric organic crystal of phenazine and chloranilic acid

Lee, Kyuho; Kolb, Brian; Thonhauser, Timo; Vanderbilt, David; Langreth, David C.

doi:10.1103/physrevb.86.104102

Cited by 27 publications

(27 citation statements)

References 28 publications

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“…65 The C 6 coefficients were calculated directly from Eqs. (7) and (8). For all our calculations, we have used the PBE GBRV ultrasoft pseudo potentials due to their excellent transferability.…”

Section: Discussionmentioning

confidence: 99%

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van der Waals density functional with corrected C6 coefficients

2019

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The non-local van der Waals density functional (vdW-DF) has had tremendous success since its inception in 2004 due to its constraint-based formalism that is rigorously derived from a many-body starting point. However, while vdW-DF can describe binding energies and structures for van der Waals complexes and mixed systems with good accuracy, one long-standing criticism-also since its inception-has been that the C6 coefficients that derive from the vdW-DF framework are largely inaccurate and can be wrong by more than a factor of two. It has long been thought that this failure to describe the C6 coefficients is a conceptual flaw of the underlying plasmon framework used to derive vdW-DF. We prove here that this is not the case and that accurate C6 coefficient can be obtained without sacrificing the accuracy at binding separations from a modified framework that is fully consistent with the constraints and design philosophy of the original vdW-DF formulation. Our design exploits a degree of freedom in the plasmon-dispersion model ωq, modifying the strength of the long-range van der Waals interaction and the cross-over from long to short separations, with additional parameters tuned to reference systems. Testing the new formulation for a range of different systems, we not only confirm the greatly improved description of C6 coefficients, but we also find excellent performance for molecular dimers and other systems. The importance of this development is not necessarily that particular aspects such as C6 coefficients or binding energies are improved, but rather that our finding opens the door for further conceptual developments of an entirely unexplored direction within the exact same constrained-based non-local framework that made vdW-DF so successful in the first place.

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Section: Discussionmentioning

confidence: 99%

“…Appendix C: Data 23 The C6 coefficients are calculated from Eqs. (7) and (8). For each data set we give the mean deviation (MD), mean absolute deviation (MAD), mean relative deviation (MRD), and mean absolute relative deviation (MARD).…”

Section: Discussionmentioning

confidence: 99%

van der Waals density functional with corrected C6 coefficients

2019

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“…6 Proton transfer, in the form of migration, may occur in the presence of this 'low' barrier, involving a gradual shift/movement in H-atom position across the HB; this effect often occurs under an external stimulus including the application of an electric field, 7,8 or changes in pressure 9 or temperature. 10 Proton migration across SSHBs can lead to a number of potentially useful properties in solid-state materials including ferroelectric 11 or colour changing 12 behaviour. Its study can reveal insight into the occurrence of such properties and have implications in functional materials design.…”

Section: Introductionmentioning

confidence: 99%

Exploring short strong hydrogen bonds engineered in organic acid molecular crystals for temperature dependent proton migration behaviour using single crystal synchrotron X-ray diffraction (SCSXRD)

et al. 2019

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“…A delicate issue concerns the choice of the exchangecorrelation functional in the calculations because the Hbond geometry and the global proton-transfer energy barriers depend substantially on it. [36][37][38] Thus, as a first step we analyze the performance of different ab initio methods and approximations in describing the geometry and energy barriers associated to the H-bonds in the system. In doing this, we also include phenomenologically the correction to the first principles H-bond classical geometry due to quantum nuclear effects.…”

Section: Introductionmentioning

confidence: 99%

Ab initio study of the structure, isotope effects, and vibrational properties in KDP crystals

et al. 2018

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The lattice dynamics of potassium dihydrogen phosphate (KDP) and its deuterated analog DKDP was studied via first-principles DFT calculations. A thorough assessment of the quality of a wide range of functionals supplemented with the approximate inclusion of quantum nuclear effects indicated that the non-local van der Waals functional vdW-DF [M. Dion et al, Phys. Rev. Lett. 92, 246401 (2004); J. Klimeš et al, Phys. Rev. B 83, 195131 (2011)] produces the best agreement with structural data for both compounds. This enabled the calculation of full phonon dispersions in the ferroelectric phase, and hence the phonon density of states and specific heat, in excellent agreement with experimental data. Phonon bands and especially modes at the Γ-point of the Brillouin zone were classified according to their vibrational pattern. This allowed for the assignment of stretching and bending modes of the hydrogen bonds. Internal modes involving the phosphate units were identified at lower frequencies, while the lowest-lying modes were those involving the K + ion. These assignments were used to interpret infrared and Raman spectra along the c-axis, and in the perpendicular plane. Phonon modes calculated at the Γ-point showed two types of instabilities. One was a normal mode polarized along the c-axis of the crystal, while the other corresponded to a twofold degenerate mode polarized in the perpendicular plane. The former gives rise to a spontaneous polarization in the ferroelectric phase at low temperatures by coupling to an optical K +-PO − 4 stretching mode, consistently with a significant off-diagonal Born effective charge on the hydrogen atoms. A mode describing the opposite rotation of neighboring PO4 tetrahedra was also found to couple strongly to the ferroelectric mode, as this modulates the O-O distance, which determines the barrier for proton transfer. The present study suggests that a minimal model to describe isotope effects in KDP should involve at least three fully-coupled vibrational modes.

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Structure and energetics of a ferroelectric organic crystal of phenazine and chloranilic acid

Cited by 27 publications

References 28 publications

van der Waals density functional with corrected C6 coefficients

van der Waals density functional with corrected C6 coefficients

Exploring short strong hydrogen bonds engineered in organic acid molecular crystals for temperature dependent proton migration behaviour using single crystal synchrotron X-ray diffraction (SCSXRD)

Ab initio study of the structure, isotope effects, and vibrational properties in KDP crystals

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