The Lattice Vibrations of Molecular Solids

Mixing of intermolecular and intramolecular vibrations in optical phonon modes: terahertz spectroscopy and solid‐state density functional theory

“…From the energy perspective, mixing of intermolecular and intramolecular vibrations in the solid phase can be explained as follows. In general, we assume that vibrations with well‐defined origins have characteristic frequencies, and vibrations with similar characteristic frequencies may mix . Intramolecular vibrations featuring collective backbone vibrations of molecules with multistructural segments may have vibrational energies similar to intermolecular vibrations.…”

“…In general, we assume that vibrations with well-defined origins have characteristic frequencies, and vibrations with similar characteristic frequencies may mix. 5,31,32 Intramolecular vibrations featuring collective backbone vibrations of molecules with multistructural segments may have vibrational energies similar to intermolecular vibrations. Therefore, the collective intramolecular modes may mix with intermolecular vibrations.…”

Characteristics of Low-Frequency Molecular Phonon Modes Studied by THz Spectroscopy and Solid-State ab Initio Theory: Polymorphs I and III of Diflunisal

“…1,2 However, low-frequency phonon modes in more complicated molecular systems have not been fully understood yet due to the challenges in representing the subtle nature of intermolecular interactions in theory. 8,9 The advance of the solid-state density functional theory (DFT) in recent years has gradually opened the way to molecular phonon modes. 10−12 The solid-state DFT methods, implementing the periodic boundary condition and modern DFT functionals including dispersion forces, have enabled a relatively accurate representation of electronic structures of molecular crystals.…”

Low-temperature Data for Carbon Dioxide

“…Because of the intensive use of carbon dioxide in industry and research [1], it has become necessary to determine its thermodynamic, physical and chemical properties on an extended range of temperatures. Significant effort has been deployed to build up a database through observations and theoretical calculations [2][3][4][5][6][7][8][9][10][11][12][13]. From the former point of view, we mention the case of the accurate measurements due to Giauque & Egan [3] and from the latter point of view, the derivation based on the classical version of the theory of lattice dynamics, which predicts the heat capacity of carbon dioxide in the range of temperatures 15<T <50 K [5], is in a very good agreement with that obtained through observations [3].…”

“…For instance, the empirical determination of the latent heat of sublimation at low temperatures remains a major obstacle because of the difficulty in eliminating the superheating of the gas [3]. Similarly, by way of example, the lagrangian classical treatment of the two-dimensional rigid rotor is intractable and the theoretical determination of the heat capacity, mentioned above, had been made possible at only sufficiently low temperatures (T <50 K) when the harmonic approximation is valid [6]. With that said, much work has to be done in order to determine further properties of carbon dioxide particularly at low temperatures, such properties are still missing in the best compendia.…”