Hydrogen-bond structure and anharmonicity in croconic acid

Abstract

First-principles molecular dynamics simulations and neutron-scattering experiments have been employed to investigate the structure and underlying vibrational motions in croconic acid as a function of temperature over the range 4-400 K. Calculated hydroxyl-bond distances were within 4% of the experimentally determined bond lengths. Temperature-dependent structures have been explored using large-scale molecular dynamics simulations. From the calculated radial distribution functions, it is found that medium-range order associated with O···H and O···O correlations are affected by an increase in temperature, yet the characteristic long-range layered structure of this material remains unaltered. Hydrogen-bond anharmonicity has been assessed from the molecular dynamics simulations, showing a red shift of ca. 50 cm(-1) of the O-H stretch frequency relative to quasi-harmonic results. This shift shows the importance of anharmonic corrections on hydrogen bonds in solid croconic acid.

Identification of normal modes responsible for ferroelectric properties in organic ferroelectric CBDC

“…This result shows that incorporation of dispersion corrections is essential to predict the structure accurately for the CBDC crystal. The difference between PBE and PBE+D calculations is consistent with the results obtained previously for croconic acid [10]. Calculations on CBDC using PBE functional published earlier does not report calculated lattice parameters, and so, a comparison with the results [11] is not possible.…”

“…From figure 3, it is clear that the doublet at 900 cm −1 , which is similar to that observed in the INS spectrum of croconic acid, (C)-O, respectively (See figure 4). The magnitudes of blueshifts in these modes are similar to those found in croconic acid [9,10] Calculations predict that the broad hump observed in INS just above 1200 cm −1 is part of the triplet which in the calculated spectrum is blue shifted to 1300 cm −1 . Modes associated with the triplet are in-pane bending of O-H-O as mentioned above, twisted motion of H(B)-C-H(B) at the base of C-ring, and librational motion of H(B), respectively.…”

“…[7][8][9][10] is blue shifted by about 150 cm −1 in the calculated spectra. These dominant vibrations, as observed in INS at 880 and 900 cm −1 , are predicted as the out-of-plane bending modes of protons for O-H(T)-O and O-H…”

“…Strong and flexible hydrogen bonds in croconic acid crystal support a Jahn-Teller type distortion leading to strong polarisation at room temperatures [7]. Inelastic neutron scattering (INS) along with first principles density functional theory (DFT) based lattice and molecular dynamics calculations help to underpin the dynamics of protons of its hydrogen bonds [8][9][10]. As a continuation of these investigations, in this article the focus is to investigate the vibrational modes related to hydrogen bonds in CBDC (1-cyclobutene-1,2dicarboxylic acid, C 6 H 8 O 4 ), another hydrogen-bonded molecular crystal showing ferroelectric properties at room temperatures [2,4].…”

A modern approach to QENS data analysis in Mantid

“…Dynamics in 2,4,5, Tri Bromo ImidazoleWith the confidence of the quality of implementation, the QENS data analysis interface is used to investigate the dynamics in organic ferroelectric material 2, 4, 5Br 3 imidazole[34]. The dynamics of protons in such ferroelectric materials are important to understand the mechanism of ferroelectricity at room temperatures [35][36][37][38]…”