Speaker
Description
Accuracy and sophistication of in silico models of structure, internal dynamics and cohesion of molecular materials at finite-temperatures has evolved over time. It has become possible to perform ab initio predictions of polymorphism of crystals of small molecules with a qualitative accuracy. Obviously, it is essential to properly capture all the non-covalent interactions within the lattice of a molecular crystal to be able to predict its lattice energy, thermodynamic properties, or even relative stabilities of multiple polymorphs. Extending the applicability of such first-principles models to larger systems with a real-life significance, such as pharmaceuticals or semiconductors is now vital for material research.
Efficient and accurate computational models of polymorphism would enable to perform an initial high-throughput screening when designing novel molecular materials. Development of such methods still represents a massive challenge to be tackled by computational chemists. This work presents a novel composite method that combines the computational efficiency of density-functional tight binding (DFTB) methods with the accuracy of density functional theory (DFT). Following the quasi-harmonic approximation, it uses a fast method to perform the otherwise costly scans of how static and dynamic cohesive characteristics of the crystal vary with respect to its volume. Such data are subsequently corrected to agree with results of a higher-level more expensive model, which needs to be evaluated only at a single volume of the crystal. It thus enables predictions of structural, cohesive and thermodynamic properties of complex molecular materials, such as pharmaceuticals or organic semiconductors, at a fraction of the original computational cost.
As the composite model retains the solid physical background, it suffers from a minimum accuracy deterioration when compared to the full treatment with the costly approach. The novel methodology is demonstrated to provide consistent predictions of structural and thermodynamic properties of real-life molecular crystals of selected pharmaceuticals and their polymorph ranking.
