Partitioning of interaction-induced nonlinear optical properties of molecular complexes. I. Hydrogen-bonded systems

Abstract

Understanding the effects of different fundamental intermolecular interactions on nonlinear optical properties is crucial for proposing efficient strategies to obtain new materials with tailored properties. In this study, we computed the electronic and vibrational (hyper)polarizabilities of ten hydrogen-bonded molecular complexes employing the MP2, CCSD and CCSD(T) methods combined with the aug-cc-pVTZ basis set. The vibrational contributions to hyperpolarizabilities included nuclear-relaxation anharmonic corrections. The effect of intermolecular interactions was analyzed in terms of excess properties, which are defined as the difference between a property of the complex and the net properties of the noninteracting subsystems. Considering systems covering a wide range of hydrogen bond strengths, the electronic and vibrational excess (hyper)polarizabilities were decomposed into different interaction energy contributions (electrostatic, exchange, induction and dispersion). This systematic study, the very first of this kind, revealed that the physical origins of the electronic and vibrational excess properties are completely different. In the case of vibrational contributions, the decomposition pattern is very similar for the polarizability and first and second hyperpolarizabilities. The exchange contributions to excess vibrational properties are the largest and they have an opposite sign to the electrostatic, induction and dispersion terms. On the other hand, no general patterns can be established for the electronic excess properties.

Partitioning of interaction-induced nonlinear optical properties of molecular complexes. II. Halogen-bonded systems

“…† correlation, incorrectly predicts the complexes HBrÁ Á ÁNCH, Br 2 Á Á ÁNCH and I 2 Á Á ÁNCH to be unbound. In this respect, the current set of XB systems qualitatively differs from a previously studied group of HB complexes, 37 in which the two first-order perturbation theory terms (i.e., electrostatic and exchange repulsion) canceled each other out to a large extent and the overall stabilization was mainly due to the negative delocalization and dispersion components. The larger role of the exchange-repulsion in the case of XB systems compared to HB complexes is related to the presence of lone pairs on the halogen atoms, which are close to the lone pair of the XB acceptor.…”

“…However, although their contributions are rather system-dependent (see also Table S6, ESI †), the exchange-repulsion and delocalization terms play a more important role, as compared to HB systems. 37 For all the complexes except HBrÁ Á ÁNCH and HIÁ Á ÁNCH, the contribution of the latter to the total excess value is larger than 24%. The role of the exchange repulsion is smaller, although when the X atom is iodine, and the A atom is I, Br or Cl, the exchange contribution is still around 20%.…”

“…Our strategy for computing the properties of interest closely follows the procedure described in our previous works on HB systems. 36,37 Therefore, here we only provide definitions of quantities discussed later in this study.…”

“…These findings were later confirmed by a more extensive study including ten hydrogen-bonded (HB) systems. 37 Let us recall that no such regularity has ever been observed in the case of electronic excess higher-order properties.…”

Partitioning of the interaction‐induced polarizability of molecules in helium environments

“…The studies conducted so far were focused on the analysis of electronic interaction‐induced electric properties. However, more recently, Zaleśny et al presented a new scheme which allows for the decomposition of not only electronic but also vibrational interaction‐induced (hyper)polarizabilities 72 . In the field of spatial confinement the decomposition of the interaction‐induced electric properties of LiH embedded in nanotube‐like and fullerene‐like helium clusters was performed by Kaczmarek and Bartkowiak 8 .…”