Molecular crystals encompass materials with extremely different properties. Ubiquitous existence of polymorphs, cocrystals or crystalline solvates further enrich the vast field of research. A delicate interplay of non-covalent interactions in the crystal lattice predetermines the material properties. Cohesive energy is the key property of each crystal, expressing how strongly the molecules hold together. Combining it with phonons enables to predict many valuable thermodynamic characteristics, such as the heat of sublimation, phase transition temperature or the stability of the given phase at given conditions. Recent advent of the computational chemistry has enabled to predict many properties of molecular crystals with a sufficient accuracy, often approaching the uncertainty level of the experiments. A combination of periodic density functional theory (DFT) calculations, ab initio wavefunction methods and the quasi-harmonic approximation has established as the workhorse of our first-principles predictions of cohesive properties of molecular crystals.<br/>Performance and computational uncertainties of the predictions of the finite-temperature sublimation enthalpies and pressures or polymorphic phase diagrams are investigated in this work. Development of our computational methodologies, based on DFT optimization of the unit-cell and molecular geometries and subsequent ab initio refinement of electronic energies, is emphasized in this context. The hybrid many-body interaction model, combining ab initio short-range and cheaper long-range regimes of treatment of molecular interactions, is used. The current story starts with the polymorphism of solid methanol. A qualitative prediction of the phase diagram of its 3 polymorphs was achieved by combining the coupled clusters with periodic Hartree-Fock calculations, reaching the computational accuracy well in the sub-kJ/mol range. A partly blind test of predictions of the sublimation data and proton transfer energies for the whole set of 20 proteinogenic amino acids followed with a fair success. For more complex systems such as crystalline ionic liquids, cheaper dispersion-corrected perturbative MP2C methods coupled with polarizable force field or with hybrid-functional based periodic DFT proved to yield valuable results, which are extremely difficult to obtain experimentally. Counterintuitively, the increasing rate of ionicity in these crystals does not grant a higher accuracy of the calculations.

Cohesion of crystalline materials from first-principles: From solid methanol to crystals of ionic liquids

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.