First Principles Simulations of Optical Rotation of Chiral Molecular Crystals

15 July 2024, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

In this work, we present simulations of the optical rotation (OR) for five molecular crystals at density functional theory level with periodic boundary conditions (DFT-PBC). Calculations are compared with experimental measurements and show semi-quantitative agreement with experimental data for three of the crystals: tartatic acid, benzil, and pentaerythritol. For the other two crystals, aspartic acid and glutamic acid, the calculated data are in qualitative agreement with, but two orders of magnitude smaller than, the experimental data. We provide some arguments that support the theoretical predictions and suggest that the experiments should be revisited. We also find that the position of H centers provided in experimental X-ray data is not sufficiently reliable for simulating OR, and better results are obtained when H atoms are allowed to relax while keeping heavier elements fixed at the experimental positions. Comparison with molecular cluster calculations with a better functional and a larger basis set indicate that the role of intermolecular interactions (reproduced with the PBC technique) is as or more important than the choice of model chemistry. Despite the current limitations in the level of theory that can be employed, these simulations provide a promising avenue to investigate the effect of intermolecular interactions on this sensitive electronic property of molecules and materials.

Keywords

Optical Rotation
Chiral Crystals
Periodic Boundary Conditions
Density Functional Theory

Supplementary materials

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Supporting Information
Description
The SI includes tables with all calculated and experimental OR data for the five crystals (Tables S1-S5) and the birefringence and angle $2\theta$ for the unit cell molecular cluster calculations of tartaric acid, using the MVG approach and the geometry with relaxed H atoms (Table S6).
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H-relaxed geometries
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This file contains the geometries of the five crystals (in cif file format) where the H positions were optimized at HSE06/6-31G(d) level of theory.
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