Accurate Atom–Dipole Interaction Model for Prediction of Electro-optical Properties: From van der Waals Aggregates to Covalently Bonded Clusters

Abstract

This work aims at the accurate estimation of the electrooptical properties of atoms and functional groups in organic crystals. A better understanding of the nature of building blocks and the way they interact with each other enables more efficient prediction of self-assembly, and thus physical properties in condensed matter. We propose a modified version of an atom−dipole interaction model that is based on atomic dipole moments calculated from the quantum theory of atoms in molecules. The method is very reliable for the prediction of various optical and electric properties in diverse chemical environments, ranging from hydrocarbon molecules bonded by dispersive interactions to polar rings connected by hydrogen bonds, or even polymeric structures whose monomers are covalently linked. Distributed polarizabilities and electrostatic potentials are compared to those obtained using a complete quantum-mechanical approach on finite-size aggregates. Our electrostatic approximation recovers isotropic polarizabilities with an accuracy of ca. 5 au and electrostatic potentials of ca. 0.05 au, even in the worst-case scenario in which polarization and chargetransfer effects are large. Functional groups are highly exportable, estimating the properties of small peptides and polyaromatics with a maximum deviation as low as ca. 15%.

Benchmark of a functional-group database for distributed polarizability and dipole moment in biomolecules

“…The importance of taking into account both inter-and intramolecular chemical environments of a building block when estimating the opto-electronic properties of molecular biomaterials from transferable functional groups was discussed in our previous works. 33,34 Covalent bonds are certainly the most relevant interactions to be considered in case highly accurate polarizability tensors are desired. Intermolecular contacts, on the other hand, such as hydrogen bonds or other noncovalent contacts, play a smaller role and therefore can be efficiently taken into account by means of semi-empirical approaches such as a DIM.…”

“…32 We have built a modified version of DIM which employs a distributed functional-group algorithm. 33,34 Here, we propose a systematic building-block database for estimating electro-optical properties of biomolecules, particularly proteins, in both gas and condensed phase. Given the importance of aqueous medium in biochemistry, the database entries are suitable for biomolecules solvated with water.…”

A building‐block database of distributed polarizabilities and dipole moments to estimate optical properties of biomacromolecules in isolation or in an explicitly solvated medium

“…In previous works, 14,15 we have benchmarked 30 DFT functionals for their performance on estimating molecular distributed polarizabilities and atomic tensors against CCSD reference calculations using the aug-cc-pVDZ basis set. Functionals of the M06 class, in particular M06-HF, proved to be very useful to reproduce CCSD results and were chosen here for further calculations.…”

“…The importance of taking into account the chemical environment of a functional group when trying to estimate electro‐optical properties of molecular materials from transferable sub‐units was discussed in our previous works 14,15 . Covalent bonds and the strongest hydrogen bonding interactions proved to be the most relevant perturbations to be accounted in case highly accurate molecular polarizability tensors are desired.…”

“…The importance of taking into account the chemical environment of a functional group when trying to estimate electro-optical properties of molecular materials from transferable sub-units was discussed in our previous works. 14,15 Covalent bonds and the strongest hydrogen bonding interactions proved to be the most relevant perturbations to be accounted in case highly accurate molecular polarizability tensors are desired. When transferable functional groups were extracted from amino acids or amino acid residuals, we needed to use an atom-dipole interaction model to semi-empirically correct for environment effects in a set of polymers and molecular aggregates.…”