Intermolecular Separation Research Articles

Interaction of a Ni(II) tetraazaannulene complex with elongated fullerenes as simple models for carbon nanotubes.

Nickel(II) complex of 5,14-dihydro-6,8,15,17-tetramethyldibenzo[b,i][1,4,8,11] tetraazacyclotetradecine (NiTMTAA), which can be employed for noncovalent functionalization of carbon nanotubes (CNTs), represents a more complex and interesting case in terms of structure of the resulting nanohybrids, as compared to the related materials functionalized with porphyrins and phthalocyanines. Due to its saddle shape, the NiTMTAA molecule adsorbed can adopt different, energetically non-equivalent orientations with respect to CNT, depending on whether CH3 or C6H4 groups contact the latter. The main goal of the present work was to provide information on the interactions of NiTMTAA with simple single-walled CNT (SWNT) models accessible for dispersion-corrected DFT calculations. For reasons of comparison, we employed three such functionals: M06-2X and LC-BLYP as implemented in Gaussian 09 package, and PBE-G as implemented in Materials Studio 6.0. In order to roughly estimate the effect of nanotube chirality on the interaction strenght, we considered two short closed-end SWNT models (also referred to as 'elongated fullerenes'), one armchair and one zigzag, derived from C60 and C80 hemispheres. In addition, we calculated similar complexes with C60, as well as I h and D 5h isomers of C80. The results were analyzed in terms of optimized geometries, formation energies, HOMO-LUMO gap energies, and intermolecular separations. Graphical Abstract Interaction of Ni(II) tetraazaannulene complex with elongated fullerenes.

Beyond Energies: Geometries of Nonbonded Molecular Complexes as Metrics for Assessing Electronic Structure Approaches.

Electronic structure approaches for calculating intermolecular interactions have traditionally been benchmarked almost exclusively on the basis of energy-centric metrics. Herein, we explore the idea of utilizing a metric related to geometry. On a diverse series of noncovalently interacting systems of different sizes, from the water dimer to the coronene dimer, we evaluate a variety of electronic structure approximations with respect to their abilities to reproduce coupled-cluster-level geometries. Specifically, we examine Hartree-Fock, second-order Møller-Plesset perturbation theory (MP2), attenuated MP2, scaled MP2, and a number of density functionals, many of which include empirical or nonempirical van der Waals dispersion corrections. We find a number of trends that transcend system size and interaction type. For instance, functionals incorporating VV10 nonlocal correlation tend to yield highly accurate geometries; ωB97X-V and B97M-V, in particular, stand out. We establish that intermolecular distance, as measured by, e.g., the center-of-mass separation of two molecules, is the geometric parameter that deviates most profoundly among the various methods. This property of the equilibrium intermolecular separation, coupled with its accessibility via a small series of well-defined single-point calculations, makes it an ideal metric for the development and evaluation of electronic structure methods.

Exciton analysis of many-body wave functions: Bridging the gap between the quasiparticle and molecular orbital pictures

Exciton sizes and electron-hole binding energies, which are central properties of excited states in extended systems and crucial to the design of modern electronic devices, are readily defined within a quasiparticle framework but are quite challenging to understand in the molecular-orbital picture. The intent of this work is to bridge this gap by providing a general way of extracting the exciton wave function out of a many-body wave function obtained by a quantum chemical excited-state computation. This methodology, which is based on the one-particle transition density matrix, is implemented within the ab initio algebraic diagrammatic construction scheme for the polarization propagator and specifically the evaluation of exciton sizes, i.e., dynamic charge separation distances, is considered. A number of examples are presented. For stacked dimers it is shown that the exciton size for charge separated states corresponds to the intermolecular separation, while it only depends on the monomer size for locally excited states or Frenkel excitons. In the case of conjugated organic polymers, the tool is applied to analyze exciton structure and dynamic charge separation. Furthermore, it is discussed how the methodology may be used for the construction of a charge-transfer diagnostic for time-dependent density-functional theory.

ProcessPIXEL: a program to generate energy-vector models from Gavezzotti'sPIXELcalculations

A command-line program is presented to convert the output from Gavezzotti'sPIXELcalculations to Shishkin's energy-vector models representing the intermolecular interaction topology. The output models comprise sets of vectors joining the centres of the molecules in a crystal structure, scaled so that the vector representing the most stabilizing pairwise interaction has length equal to half of the corresponding intermolecular separation. When the energy-vector model is packed, the most stabilizing pairwise interaction is represented as a continuous line between interacting molecules, while the other intermolecular interactions are shown as discontinuous lines, with a smaller gap representing a more stabilizing interaction. The energy-vector models can be overlaid on the crystal structure using theMercuryvisualizer to enable convenient visualization of structural motifs that contribute significantly to the overall crystal packing energy.

First-principles description of charge transfer in donor-acceptor compounds from self-consistent many-body perturbation theory

We investigate charge transfer in prototypical molecular donor-acceptor compounds using hybrid density functional theory (DFT) and the GW approximation at the perturbative level (G0W0) and at full self-consistency (sc-GW). For the systems considered here, no charge transfer should be expected at large intermolecular separation according to photoemission experiment and accurate quantum-chemistry calculations. The capability of hybrid exchange-correlation functionals of reproducing this feature depends critically on the fraction of exact exchange $\alpha$, as for small values of $\alpha$ spurious fractional charge transfer is observed between the donor and the acceptor. G0W0 based on hybrid DFT yields the correct alignment of the frontier orbitals for all values of $\alpha$. However, G0W0 has no capacity to alter the ground-state properties of the system, because of its perturbative nature. The electron density in donor-acceptor compounds thus remains incorrect for small $\alpha$ values. In sc-GW, where the Green's function is obtained from the iterative solution of the Dyson equation, the electron density is updated and reflects the correct description of the level alignment at the GW level, demonstrating the importance of self-consistent many-body approaches for the description of ground- and excited-state properties in donor-acceptor systems.

Do Fullerene Superconductors Belong to the High-Tc Superconductivity Universe?

A3C60 (A = alkali metal) superconductors were known to adopt face-centred cubic (fcc) structures with their superconducting Tc increasing monotonically with increasing interfullerene spacing, reaching a 33 K maximum for RbCs2C60 – this physical picture had remained unaltered since 1992. Trace superconductivity (s/c fraction<0.1%) at 40 K under pressure was also reported in 1995 in multiphase samples with nominal composition Cs3C60. Despite numerous attempts by many groups worldwide, this remained unconfirmed and the structure and composition of the material responsible for superconductivity unidentified. Thus the possibility of enhancing fulleride superconductivity and understanding the structures and properties of these archetypal molecular solids had remained elusive. Here I will present our recent progress in this field in accessing high-symmetry hyperexpanded alkali fullerides in the vicinity of the Mott-Hubbard metal-insulator boundary and at previously inaccessible intermolecular separations. The physical picture that emerges for the alkali fullerides is that, contrary to long-held beliefs, they are the simplest members of the high-Tc superconductivity family. We demonstrated this by showing that in the two hyperexpanded Cs3C60 polymorphs (fcc- and A15-structured) [1-3], superconductivity emerges upon applied pressure out of an antiferromagnetic insulating state and displays an unconventional behaviour – a superconductivity dome – explicable by the prominent role of strong electron correlations.

Interaction of the beryllium cation with molecular hydrogen and deuterium.

The structural and spectroscopic properties of the Be(+)-H2 and Be(+)-D2 electrostatic complexes are investigated theoretically. A three-dimensional ground-state potential energy surface is generated ab initio at the CCSD(T) level and used for calculating the lower rovibrational energy levels variationally. The minimum of the potential energy surface corresponds to a well depth of 3168 cm(-1), an intermolecular separation of 1.776 Å, with the bond of the H2 subunit being 0.027 Å longer than for the free molecule. Taking vibrational zero point energy into account, the complexes containing para H2 and ortho D2 are predicted to have dissociation energies of 2678 and 2786 cm(-1), respectively. The νHH band of Be(+)-H2 is predicted to be red-shifted from the free dihydrogen transition by -323 cm(-1), whereas the corresponding shift for Be(+)-D2 is predicted to be -229 cm(-1). The dissociation energy of the Be(+)-D2 complex is calculated to be slightly higher than the energy required to vibrationally excite the D2 subunit, raising the possibility that the onset of dissociation can be observed in the infrared predissociation spectrum at a particular rotational energy level in the νDD manifold.

Infrared spectra of He–, Ne–, and Ar–C6D6

Spectra of He–, Ne– and Ar–C6D6 in the region of the ν12 fundamental of C6D6 are observed in a pulsed supersonic jet expansion using a tunable optical parametric oscillator laser source. These are the first reported infrared spectra of rare gas–benzene complexes and the first observation in any region for He– and Ne–C6D6. Two bands are studied for each complex: the ν12 fundamental itself (≈2289cm−1) and the ν2+ν13 combination band (≈2276cm−1) which are coupled by a Fermi resonance. Effective intermolecular separations of 3.593(1) and 3.455(1)Å are obtained for He– and Ne–C6D6, respectively, consistent with previous ultraviolet and microwave results for the analogous C6H6 complexes.

Ion-Molecule Clustering in Differential Mobility Spectrometry: Lessons Learned from Tetraalkylammonium Cations and their Isomers

Differential mobility spectrometry (DMS) can distinguish ions based upon the differences in their high- and low-field ion mobilities as they experience the asymmetric waveform applied to the DMS cell. These mobilities are known to be influenced by the ions' structure, m/z, and charge distribution (i.e., resonance structures) within the ions themselves, as well as by the gas-phase environment of the DMS cell. While these associations have been developed over time through empirical observations, the exact role of ion structures or their interactions with clustering molecules remains generally unknown. In this study, that relationship is explored by observing the DMS behaviors of a series of tetraalkylammonium ions as a function of their structures and the gas-phase environment of the DMS cell. To support the DMS experiments, the basin-hopping search strategy was employed to identify candidate cluster structures for density functional theory treatment. More than a million cluster structures distributed across 72 different ion-molecule cluster systems were sampled to determine global minimum structures and cluster binding energies. This joint computational and experimental approach suggests that cluster geometry, in particular ion-molecule intermolecular separation, plays a critical role in DMS.

Density functional theory study of the dipole across the P3HT : PCBM complex: the role of polarization and charge transfer

Using density functional theory (DFT) calculations we study the electronic structure and the dipole moment of the complex formed by an oligomer of poly(3-hexylthiopene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). We scanned the total energy of the P3HT : PCBM dimer as a function of the relative angular orientation between the two molecules in the search for stable angular configurations. After finding four stable geometries, we applied DFT calculations to characterize the electronic properties of those configurations. Using extended charge decomposition analysis, we calculated the contributions of the occupied and unoccupied orbitals from the individual species to form the electronic states of the complex. This method allowed us to determine the charge effectively transferred from the polymer to the PCBM upon the formation of the complex. Our results indicate that this amount of transferred charge is small but extremely sensitive to the detailed arrangement of the molecules in the dimer. However, the direction of the dipole moment of the complex is strongly influenced by the orientation of the permanent dipole of the PCBM relative to the chain of the oligomer. In the light of the dipole-assisted exciton dissociation models, we identified only one configuration that has a dipole moment with the right orientation to help the dissociation of a photo-excited electron–hole pair in the polymer. This configuration is just the molecular arrangement with the lowest total energy. Moreover, we study the contributions of charge transfer and electronic polarization to the composition of this dipole as a function of the intermolecular separation. We finally discuss how the results found using our simple dimer model can be related to electronic properties obtained using more-realistic models of the P3HT/PCBM interface.

Communication: ab initio simulations of hydrogen-bonded ferroelectrics: collective tunneling and the origin of geometrical isotope effects.

Ab initio simulations that account for nuclear quantum effects have been used to examine the order-disorder transition in squaric acid, a prototypical H-bonded antiferroelectric crystal. Our simulations reproduce the >100 K difference in transition temperature observed upon deuteration as well as the strong geometrical isotope effect observed on intermolecular separations within the crystal. We find that collective transfer of protons along the H-bonding chains - facilitated by quantum mechanical tunneling - is critical to the order-disorder transition and the geometrical isotope effect. This sheds light on the origin of isotope effects and the importance of tunneling in squaric acid which likely extends to other H-bonded ferroelectrics.

A revisitation of the Förster energy transfer near a metallic spherical nanoparticle: (1) Efficiency enhancement or reduction? (2) The control of the Förster radius of the unbounded medium. (3) The impact of the local density of states

The central motivation of this theoretical revisitation comes from the fact that some experimental works about Förster energy transfer report improvement of the Förster efficiency when the donor-acceptor molecular pair is in the vicinity of a metallic particle, while others found efficiency deterioration. In the presence of a nanoscale metallic sphere, we calculate contour plots of the Förster energy transfer rate KF and the Förster efficiency η as a function of the acceptor position rA for a fixed donor position. These contour plots clearly highlight the influence of the sphere on KF and η as the donor position, the orientations of donor and acceptor dipoles, and the particle size are varied; also the impact on KF(rA) and η due to the excitation of surface plasmons is easily noticeable from these contour plots. Moreover, we obtain the enhancement factor KF/KF0 (KF0 refers to the case without sphere) against the donor-surface separation for particular donor-acceptor spatial distributions, several particle sizes, and distinct molecular dipole orientations. Therefore, our calculations provide a systematic analysis of the Förster energy transfer in the presence of a metallic nanosphere. Based on these results, we formulate hypotheses for explaining the aforementioned contradictory experimental results about η. To complement our study, we examine the impact of the local density of states ρ on KF. KF is practically unperturbed by sphere when the intermolecular separation R is ≲ 3 nm, since the direct donor-acceptor electromagnetic interaction is dominant. On the contrary, when R ≳ 3 nm, the nanosphere perturbs KF and this perturbation is stronger if plasmonic resonances are excited. KF/KF0 can greatly be enhanced in certain regions, but these regions coincide with low-efficiency regions, compromising applications involving the Förster process. In the presence of the nanosphere, the high Förster efficiency region (η ≥ 0.5) has the same shape as that for the case without sphere, but its extension (Förster radius Ro) is reduced; this effect is a consequence of the large increase of the donor direct decay rate and Ro depends strongly on donor position. Consequently, the sphere controls Ro that is associated with the efficiency pattern that corresponds to the unbounded medium; this effect can be exploited in the measuring technique of nanoscale displacements of proteins that is based on the fluorescence resonant energy transfer. The functional form of KF(ρ) is determined by the intermolecular separation R, the spatial configuration and the dipole orientations of the molecular pair, and the donor proximity to the nanoparticle.

A new ab initio potential energy surface for the collisional excitation of HCN by para- and ortho-H2

We present a new four-dimensional potential energy surface for the collisional excitation of HCN by H2. Ab initio calculations of the HCN-H2 van der Waals complex, considering both molecules as rigid rotors, were carried out at the explicitly correlated coupled cluster with single, double, and perturbative triple excitations [CCSD(T)-F12a] level of theory using an augmented correlation-consistent triple zeta (aVTZ) basis set. The equilibrium structure is linear HCN-H2 with the nitrogen pointing towards H2 at an intermolecular separation of 7.20 a0. The corresponding well depth is -195.20 cm(-1). A secondary minimum of -183.59 cm(-1) was found for a T-shape configuration with the H of HCN pointing to the center of mass of H2. We also determine the rovibrational energy levels of the HCN-para-H2 and HCN-ortho-H2 complexes. The calculated dissociation energies for the para and ortho complexes are 37.79 cm(-1) and 60.26 cm(-1), respectively. The calculated ro-vibrational transitions in the HCN-H2 complex are found to agree by more than 0.5% with the available experimental data, confirming the accuracy of the potential energy surface.

Self-Assembly Properties of Semiconducting Donor–Acceptor–Donor Bithienyl Derivatives of Tetrazine and Thiadiazole—Effect of the Electron Accepting Central Ring

Scanning tunneling microscopy was used to study the effect of the electron-accepting unit and the alkyl substituent's position on the type and extent of 2D supramolecular organization of penta-ring donor-acceptor-donor (DAD) semiconductors, consisting of either tetrazine or thiadiazole central acceptor ring symmetrically attached to two bithienyl groups. Microscopic observations of monomolecular layers on HOPG of four alkyl derivatives of the studied adsorbates indicate significant differences in their 2D organizations. Ordered monolayers of thiadiazole derivatives are relatively loose and, independent of the position of alkyl substituents, characterized by large intermolecular separation of acceptor units in the adjacent molecules located in the face-to-face configuration. The 2D supramolecular architecture in both derivatives of thiadiazole is very sensitive to the alkyl substituent's position. Significantly different behavior is observed for derivatives of tetrazine (which is a stronger electron acceptor). Stronger intermolecular DA interactions in these adsorbates generate an intermolecular shift in the monolayer, which is a dominant factor determining the 2D structural organization. As a consequence of this molecular arrangement, tetrazine groups (A segments) face thiophene rings (D segments) of the neighboring molecules. Monolayers of tetrazine derivatives are therefore much more densely packed and characterized by similar π-stacking of molecules independently of the position of alkyl substituents. Moreover, a comparative study of 3D supramolecular organization, deduced from the X-ray diffraction patterns, is also presented clearly confirming the polymorphism of the studied adsorbates.

Crystal structure versus charge transport in organic single crystals of [1]benzothieno[3,2-b][1]benzothiophene derivatives from a multiscale theoretical study

[1]Benzothieno[3,2-b][1]benzothiophene derivatives with high air stability have recently displayed excellent charge transport properties in field-effect devices. In particular, the average charge mobilities can reach as high as 16.4 ± 6.1 cm2 V−1 s−1 in devices with a high quality semiconductor/insulator interface, which is comparable to the performance for a rubrene single-crystal device. To better understand these excellent charge transport properties, a multiscale approach combining molecular dynamics and quantum-chemical calculations was used in this work to assess the structure–property relationship for three of the [1]benzothieno[3,2-b][1]benzothiophene derivatives with different alkyl side chains. It is indicated that the extremely large electronic couplings along the a-axis direction are responsible for the excellent charge transport properties in these systems. While the molecular packings are centrosymmetrical in the ab plane, the lattice vibrations were found to hamper the charge transport in optimized crystal structures at the COMPASS molecular mechanics level which is opposite to the recent findings that the lattice dynamics should have a negligible effect on the charge mobility in the centrosymmetrical plane. The reason for such behavior was analyzed and the predicted order of the overall charge mobilities for the studied systems was consistent with the experiments. Meanwhile, how well the force field reproduces the observed crystal structures and dimer intermolecular separations and orientations is discussed in this work. In addition, it is shown that the present charge transport model can not only predict the magnitude of the charge mobility but also the measured “band-like” charge transport in experiments, so the nuclear tunneling effect is very important for charge transport in organic semiconductors as was demonstrated in recent theoretical work.

Charge Transfer from Regularized Symmetry-Adapted Perturbation Theory.

The charge-transfer (CT) together with the polarization energy appears at second and higher orders in symmetry-adapted perturbation theory (SAPT). At present there is no theoretically compelling way of isolating the charge-transfer energy that is simultaneously basis-set independent and applicable for arbitrary intermolecular separation. We argue that the charge-transfer can be interpreted as a tunneling phenomenon and can therefore be defined via regularized SAPT. This leads to a physically convincing, basis-independent definition of the charge-transfer energy that captures subtleties of the process, such as the asymmetry in the forward and backward charge transfer, as well as secondary transfer effects. With this definition of the charge-transfer the damping needed for polarization models can be determined with a level of confidence hitherto not possible.

Pressure Induced Crossover between a Ferromagnetic and a Canted Antiferromagnetic State for [Bis(pentamethylcyclopentadienyl)-iron(III)][Tetracyanoethenide], [FeCp2*][TCNE

The reversible hydrostatic pressure dependent DC magnetic behavior of the ferromagnetically ordered electron transfer salt [Fe(III)Cp2*](•+)[TCNE](•-) (Cp* = pentamethylcyclopentadienide; TCNE = tetracyanoethylene) was studied up to 12.2 kbar. A significant departure from the ambient pressure ferromagnetic behavior was observed under pressure. The temperature dependent magnetization data were typical of a ferromagnet at ambient pressure but exhibited an extreme reduction with increasing applied pressure, while metamagnetic-like behavior was evident in the field dependent magnetization data at 4.2 kbar and above. Hence, the decrease of the intermolecular separations due to increasing pressure enhances the nearest neighbor couplings, leading to an increase in magnetic ordering temperature, T(c). Furthermore, the presence of a metamagnetic-like behavior suggests an increase of the antiferromagnetic contribution to the interchain interactions. The low field magnetization data indicate that spin canting is induced by pressure, leading to a canted antiferromagnetic phase with a much lower magnetization than the low-pressure ferromagnetic state. This unprecedented magnetic behavior is consistent with the field, temperature, and pressure dependences of the magnetization below 20 K.

Optimal geometries and harmonic vibrational frequencies of the global minima of water clusters (H2O)n, n = 2–6, and several hexamer local minima at the CCSD(T) level of theory

We report the first optimum geometries and harmonic vibrational frequencies for the ring pentamer and several water hexamer (prism, cage, cyclic and two book) at the coupled-cluster including single, double, and full perturbative triple excitations (CCSD(T))/aug-cc-pVDZ level of theory. All five examined hexamer isomer minima previously reported by Møller-Plesset perturbation theory (MP2) are also minima on the CCSD(T) potential energy surface (PES). In addition, all CCSD(T) minimum energy structures for the n = 2-6 cluster isomers are quite close to the ones previously obtained by MP2 on the respective PESs, as confirmed by a modified Procrustes analysis that quantifies the difference between any two cluster geometries. The CCSD(T) results confirm the cooperative effect of the homodromic ring networks (systematic contraction of the nearest-neighbor (nn) intermolecular separations with cluster size) previously reported by MP2, albeit with O-O distances shorter by ~0.02 Å, indicating that MP2 overcorrects this effect. The harmonic frequencies at the minimum geometries were obtained by the double differentiation of the CCSD(T) energy using an efficient scheme based on internal coordinates that reduces the number of required single point energy evaluations by ~15% when compared to the corresponding double differentiation using Cartesian coordinates. Negligible differences between MP2 and CCSD(T) frequencies are found for the librational modes, while uniform increases of ~15 and ~25 cm(-1) are observed for the bending and "free" OH harmonic frequencies. The largest differences between CCSD(T) and MP2 are observed for the harmonic hydrogen bonded frequencies, for which the former produces larger absolute values than the latter. Their CCSD(T) redshifts from the monomer values (Δω) are smaller than the MP2 ones, due to the fact that CCSD(T) produces shorter elongations (ΔR) of the respective hydrogen bonded OH lengths from the monomer value with respect to MP2. Both the MP2 and CCSD(T) results for the hydrogen bonded frequencies were found to closely follow the relation -Δω = s · ΔR, with a rate of s = 20.2 cm(-1)/0.001 Å for hydrogen bonded frequencies with IR intensities >400 km/mol. The CCSD(T) harmonic frequencies, when corrected using the MP2 anharmonicities obtained from second order vibrational perturbation theory, produce anharmonic CCSD(T) estimates that are within <60 cm(-1) from the measured infrared (IR) active bands of the n = 2-6 clusters. Furthermore, the CCSD(T) harmonic redshifts (with respect to the monomer) trace the measured ones quite accurately. The energetic order between the various hexamer isomers on the PES (prism has the lowest energy) previously reported at MP2 was found to be preserved at the CCSD(T) level, whereas the inclusion of anharmonic corrections further stabilizes the cage among the hexamer isomers.

Electronic excitation and structural relaxation of the adenine dinucleotide in gas phase and solution

The excited states and potential surfaces of the adenine dinucleotide are analyzed in gas phase and in solution using a correlated ab initio methodology in a QM/MM framework. In agreement with previous studies, a rather flat S1 surface with a number of minima of different character is found. Specifically, our results suggest that exciplexes with remarkably short intermolecular separation down to ~2.0 Å are formed. A detailed analysis shows that due to strong orbital interactions their character differs significantly from any states present in the Franck-Condon region. The lowest S1 energy minimum is a ππ* exciplex with only a small amount of charge transfer. It possesses appreciable oscillator strength with a polarization almost perpendicular to the planes of the two adenine molecules.

On the Origins of Large Interaction-Induced First Hyperpolarizabilities in Hydrogen-Bonded π-Electronic Complexes

In this article we elucidate the origins of interaction-induced linear and nonlinear electro-optic properties of model hydrogen-bonded π-electronic complexes. In particular we report on contributions due to various interaction energy terms to excess dipole moments (Δμ), electric dipole polarizabilities (Δα), and first hyperpolarizabilities (Δβ), focusing on the latter. The analysis of intermolecular interaction-induced electric properties is performed for selected model systems including quasi-linear dimers of urea, diformamide, 4-pyridone, 4-nitroaniline, and the complex of hydrogen fluoride with nitroacetylene. The nature of intermolecular interactions as well as of the Δμ and Δα is very similar in all studied complexes. However, partitioning of Δβ into physically well-defined components reveals that the origins of this term, the magnitude of which is often comparable to the hyperpolarizabilities of isolated monomers, are different in each case. Our results indicate that, even though hydrogen bonding usually diminishes the nonlinear response of interacting species, the first hyperpolarizability of complexes with the nitro group acting as a proton acceptor is substantially increased, essentially due to field-induced changes of electrostatic interactions between subsystems. However, in the remaining complexes the origins of Δβ are much more involved. Even though at large intermolecular separations the origins of interaction-induced electric properties are essentially due to the field-induced electrostatic and induction interactions, in the vicinity of van der Waals minimum the overlap effects cannot be neglected since they may substantially alter the predicted excess properties or even determine their magnitude and sign. On the other hand the Δβ contribution due to dispersion interactions is usually negligible. Interestingly, the values of interaction-induced first hyperpolarizability in some cases depend strongly on the intermolecular separation in the vicinity of equilibrium geometry.