First‐principles modeling of molecular crystals: structures and stabilities, temperature and pressure

Abstract

The understanding of the structure, stability, and response properties of molecular crystals at finite temperature and pressure is crucial for the field of crystal engineering and their application. For a long time, the field of crystal-structure prediction and modeling of molecular crystals has been dominated by classical mechanistic force-field methods. However, due to increasing computational power and the development of more sophisticated quantum-mechanical approximations, first-principles approaches based on density functional theory can now be applied to practically relevant molecular crystals. The broad transferability of first-principles methods is especially imperative for polymorphic molecular crystals. This review highlights the current status of modeling molecular crystals from first principles. We give an overview of current state-of-the-art approaches and discuss in detail the main challenges and necessary approximations. So far, the main focus in this field has been on calculating stabilities and structures without considering thermal contributions. We discuss techniques that allow one to include thermal effects at a first-principles level in the harmonic or quasi-harmonic approximation, and that are already applicable to realistic systems, or will be in the near future. Furthermore, this review also discusses how to calculate vibrational and elastic properties. Finally, we present a perspective on future uses of first-principles calculations for modeling molecular crystals and summarize the many remaining challenges in this field

First-Principles Models for van der Waals Interactions in Molecules and Materials: Concepts, Theory, and Applications

“…280 Thermal and pressure effects are not only crucial for the stability under thermodynamic conditions, but are also essential for the unitcell structure itself and a variety of response properties, such as vibrational spectra and elastic constants. 281 The most recent structure prediction blind test for organic crystals 282 featured a practically relevant and highly polymorphic system involving a quite flexible molecule. This flexibility leads to a much larger number of local minima within a narrow energy window compared to crystals containing only rigid molecules.…”

Solid-State Testing of a Van-Der-Waals-Corrected Exchange-Correlation Functional Based on the Semiclassical Atom Theory

“…Non-covalent interactions, especially of the van der Waals type, have been nowadays recognized as fundamental ingredients of any correct and accurate description of complex materials [1][2][3][4][5][6][7][8][9]. In fact, even if the magnitude of non-covalent forces is typically much smaller than that of iono-covalent bonds, the ubiquity of such interactions makes them significant in large systems.…”

“…For these reasons, the proper description of dispersion as well as other non-covalent forces has gained a prominent role in computational chemistry [6,[10][11][12][13][14][15][16]. Even more important is the role they play in solid-state applications where extended systems are involved, whose cohesion is not mainly determined by iono-covalent interactions [3,5,8,9,[17][18][19][20][21], e.g., layered or molecular solids.…”

Structure and Stability of Molecular Crystals with Many-Body Dispersion-Inclusive Density Functional Tight Binding

“…10,16−19 In particular, the inclusion of beyond-pairwise dispersion interactions through the many-body dispersion (MBD) method coupled to semilocal DFT functionals has proven to be successful in this context. 10,15,20 To address larger length and time scales and more efficient structure prediction, several approximate electronic structure methods have been highly successful including semiempirical quantum chemical methods such as AM1, PM7, or the DFT-based densityfunctional tight binding (DFTB). 21−23 DFTB has been significantly improved recently, particularly in its description of charge polarization via third-order charge fluctuation corrections (DFTB3) 24,25 or its description of hydrogen bonding.…”