Crystal Structure Predictions for 4-Amino-2,3,6-trinitrophenol Using a Tailor-Made First-Principles-Based Force Field

Abstract

Predictions of crystal structures from first-principles electronic structure calculations and molecular simulations have been performed for an energetic molecule, 4-amino-2,3,6trinitrophenol. This physics-based approach consists of a series of steps. First, a tailor-made two-body potential energy surface (PES) was constructed with recently developed software, autoPES, using symmetry-adapted perturbation theory based on a densityfunctional theory description of monomers [SAPT(DFT)]. The fitting procedure ensures asymptotic correctness of the PES by employing a rigorous asymptotic multipole expansion, which seamlessly integrates with SAPT(DFT) interaction energies. Next, crystal structure prediction (CSP) was performed by generating possible crystal structures with rigid molecules, minimizing these structures using the SAPT(DFT) force field, and running isothermal−isobaric molecular dynamics (MD) simulations with flexible molecules based on the tailor-made SAPT(DFT) intermolecular force field and a generic/SAPT(DFT) intramolecular one. This workflow led to the experimentally observed structure being identified as one of the forms with the lowest lattice energy, demonstrating the success of a first-principles, bottom-up approach to CSP. Importantly, we argue that the accuracy of the intermolecular potential, here the SAPT(DFT)-based potential, is determinative of the crystal structure, while generic/SAPT(DFT) force fields can be used to represent the intramolecular potential. This force field approach simplifies the CSP workflow, without significantly compromising the accuracy of the prediction.

Physical mechanisms of intermolecular interactions from symmetry-adapted perturbation theory

“…The most convincing confirmation are vibration-rotation-tunneling (VRT) spectra of dimers and trimers: spectra computed from SAPT potentials agree very well with experiment [84,[154][155][156][157]. Another example are crystal-structure predictions from SAPT-based force fields, which correctly identify the experimental crystal as one of the top-ranked polymorphs [158][159][160][161][162][163].…”

Pharmaceutical Digital Design: From Chemical Structure through Crystal Polymorph to Conceptual Crystallization Process

“…Estimating free energy differences usually relies on the identification and efficient computation of appropriate CVs, − which is increasingly problematic with more complex growth units . This currently impacts the applicability to large-scale CSP_thd studies with hundreds of radically different crystal forms.…”

Is the Local Ion Density Sufficient to Drive NaCl Nucleation from the Melt and Aqueous Solution?

“…In industrial scenarios, understanding crystallization processes is essential for improvement of material design and synthesis. For instance, lithium deposition has a significant impact on the lifetime and behavior of batteries; , the nucleation and growth of metal–organic frameworks happens in solutions but the mechanism is not clear; and active pharmaceutical ingredients also require specific crystal polymorphs. − …”