Calculation of macroscopic first- and third-order optical susceptibilities for the benzene crystal

Abstract

Starting from a set of high-level ab initio frequency-dependent molecular ®rst-and third-order polarizabilities, the macroscopic ®rst-order (linear) and third-order (cubic) susceptibilities of the benzene crystal are calculated. Environmental eects are taken into account using a rigorous local-®eld theory and are compared with the anisotropic Lorentz ®eld factor approach. The experimentally determined ®rst-order susceptibility of crystalline benzene is accurately reproduced. Dispersion curves for the ®rst-order susceptibility and results for electric-®eld-induced second-harmonic generation and third-harmonic generation experiments are predicted. Comparison with similar calculations conducted in the course of molecular simulations of liquid benzene shows that the theoretical results for the two phases are of comparable accuracy. Overall, the results show that for the fairly compact nonpolar benzene molecules, environmental eects on the eective molecular response are small.

Crystal Field Effects on Atomic and Functional-Group Distributed Polarizabilities of Molecular Materials

“…Because many molecular crystals feature only weak noncovalent intermolecular interactions, including the weakest, therefore longest version of hydrogen bonds, classical electrostatic models based on point dipoles have traditionally been adopted to estimate crystal susceptibilities from gas-phase molecular polarizabilities. − One of the most successful implementations is known as the atom–dipole interaction model (ADIM). − In this approach, the electric field experienced by a molecule within a crystal has additive contributions from the externally applied field and from the field generated by neighboring point dipoles in the lattice. Using QTAIM partitioning, the component i of the local (applied plus induced) field on the basin Ω due to all the other basins Λ in the neighborhood can be written as in which is the ij component of the dipole field tensor between the atomic basins Ω and Λ: where x ΩΛ = ( x Ω – x Λ ) is the difference in the Cartesian x coordinate between the basins Ω and Λ and r ΩΛ is the interatomic distance.…”

The Role of Hydrogen Bond in Designing Molecular Optical Materials

“…The relative accuracy of these approximations depends on the size and shape of the molecules. For small compounds, such as urea or benzene [34], RLFT1 and RLFTn do not differ substantially, whereas RLFTn is typically more accurate to describe the anisotropies of larger systems, as shown for m-nitroaniline [35].…”

“…Therefore, this approach allows the estimation of "in-crystal" dipole moments from the knowledge of the polarizability of the constituent molecules and the symmetry operations used to construct the aggregate. This formalism is usually called rigorous local field theory (RLFT) [34,35], and can be straightforwardly extended to compute atomic and functional-group induced dipole moments µ ind pΩ, kq in the k molecule of the crystal, provided that a partitioning scheme is used to calculate µpΩq and αpΩq. In this case, the molecular point-dipole realization of RLFT, i.e., the one in which each molecule is considered as a point dipole (RLFT1), would be replaced by a distributed atomic or functional-group point-dipole treatment, in which n atomic dipoles are distributed over the molecule (RLFTn).…”

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

“…Some electrostatic models − have been proposed to study interactions in molecular crystals. From the molecular dipole obtained in gas phase, one can simulate crystal field effects at least partially, as such models do not take into account electronic density polarization due to the environment.…”

“…Since intermolecular contacts are usually much weaker than the more covalent intramolecular ones, semiempirical approaches, typically based on classical electrostatics, have emerged to estimate the optical behavior of the material from gas-phase calculations in a kind of perturbed local-field correction. − All of these methods are ultimately based on the fact that the electric field experienced by a molecule in a crystal possesses additive contributions from any eventual externally applied field and from the field generated by all neighboring dipoles within the lattice, but they certainly vary in efficiency and accuracy . On the one hand, most of these implementations do not explicitly treat atoms or functional groups but tend to reduce entire molecules to point dipoles.…”