Intermolecular Dispersion Energy Research Articles

The organic co-crystals formed using naphthalenediimide-based triangular macrocycles and coronene: intermolecular charge transfers and nonlinear optical properties.

Formation of organic co-crystals is an effective strategy to synthesize near infrared emission and nonlinear optical (NLO) materials, which often show "1 + 1 > 2" performance. Moreover, the crystallization process can be effectively regulated through supramolecular interactions; thus the properties of co-crystal materials can also be flexibly regulated. Here, in order to further understand the nature and formation mechanism of co-crystals from the perspective of theoretical research, we studied the structures, intermolecular interactions, absorption spectra, charge transfer (CT) characteristics and nonlinear optical (NLO) properties of the newly synthesized organic co-crystals formed between naphthalenediimide based triangles (NDI, acceptor) and coronene (COR, donor). According to the analysis of decomposition of intermolecular interaction energy, dispersion energy played a major role, so the co-crystal properties can be regulated by regulating the intermolecular dispersion energy. More importantly, the formation of co-crystals NDI-COR and NDI-2COR reduced the Egap values with respect to those of their components. And there was significant intermolecular CT from COR to NDI and the degree of CT in NDI-COR was larger than that in NDI-2COR, so that the αtot and γtot values of NDI-COR and NDI-2COR were significantly greater than those of their components. Thus, the NLO properties of organic co-crystals can be further improved by enhancing the electron-donating ability of the donor and the electron-withdrawing ability of the acceptor to enhance the degree of intermolecular interaction energy and CT.

High Vertical Carrier Mobilities of Organic Semiconductors Due to a Deposited Laid-Down Herringbone Structure Induced by a Reduced Graphene Oxide Template.

High vertical carrier mobilities in organic semiconductor films are a challenging issue for fundamentally improving the performance of vertical devices. To achieve improvement in the vertical direction, a reduced graphene oxide (rGO) template is used with pentacene and DNTT having a herringbone structure enabling two-dimensional (2D) transport in comparison with CuPc having a slipped-stack structure. A thin-film structure and the optoelectrical properties of the oriented films are investigated with respect to molecular structures and packing modes. The rGO template induces a "laid-down" herringbone structure for pentacene and DNTT with a face-on orientation. Our results reveal that intermolecular dispersion energy is an additional important factor to form face-on states of molecules and influences face-on ratios in the films on rGO. Vertical charge mobilities of the films are significantly enhanced by the rGO template. Particularly, the DNTT film with a laid-down herringbone structure produces a vertical mobility as high as 0.27 cm2 V-1 s-1, one of the highest values for ordinary thin films with several hundred nanometer thickness. These findings suggest that 2D transport is advantageous for vertical carrier transport also.

Intermolecular dispersion energies from coupled exact-exchange Kohn-Sham excitation energies and vectors

The calculation of intermolecular dispersion energies within a time-dependent density-functional theory framework (TDDFT) is reviewed. While the commonly used route to compute dispersion energies is to employ the Casimir-Polder integral transform and thereby describing the dispersion energy as a functional of the response functions of the monomers, this alternative approach leads to a particularly simple form for the long-range interaction between two subsystems in terms of the TDDFT eigenvectors and excitation energies. We present two different schemes to reduce the high computational cost for calculating the excitation energies and vectors of the monomers to be used to compute the dispersion energies via the TDDFT method. This is achieved by a decoupling of the occupied-virtual orbital product basis functions which are associated with single-particle excitations belonging to large and small oscillator strengths. It will be shown that this approach can lead to large speedups of 90% and more compared to a full diagonalisation of the hessian, while the fully coupled dispersion energies can be reproduced with a reasonable accuracy. We also investigate the role of the dispersion energy for the description of σ- and π-stacking interactions and discuss various dispersion energy approximations, including the D3 model by Grimme.

Quasi-relativistic two-component computations of intermolecular dispersion energies

ABSTRACTA method for computing quasi-relativistic two-component dispersion energies is developed and implemented in the TURBOMOLE program package. The method is based on the Casimir–Polder formula for dispersion energies, which occurs in symmetry-adapted perturbation theory. The method is applied to evaluate the dispersion energies of a small set of van der Waals complexes involving heavy elements such as gold, mercury and bismuth.

Pair-potential approach to accurate dispersion energies between group 12 (Zn, Cd, Hg) clusters.

Dispersion interactions between group 12 (Zn, Cd, Hg) metal clusters are studied at the CCSD(T) level with triple-ζ basis sets. We use atomic orientation dependent C6 dispersion coefficients derived from simple model systems to calculate the intermolecular dispersion energy between larger metal clusters. By using an atomic pair-potential model, we are able to obtain highly accurate results comparable to the CCSD(T) level of theory. For all the systems studied, our method results in a robust description of the dispersion energy at long distances, and it is able to outperform the examined dispersion corrected DFT calculations.

Insight on the interaction of polychlorobiphenyl with nucleic acid–base

The interaction between one polychlorobiphenyl (3,3',4,4',-tetrachlorobiphenyl, coded PCB77) and the four DNA nucleic acid-base is studied by means of quantum mechanics calculations in stacked conformations. It is shown that even if the intermolecular dispersion energy is the largest component of the total interaction energy, some other contributions play a non negligible role. In particular the electrostatic dipole-dipole interaction and the charge transfer from the nucleobase to the PCB are responsible for the relative orientation of the monomers in the complexes. In addition, the charge transfer tends to flatten the PCB, which could therefore intercalate more easily between DNA base pairs. From these seminal results, we predict that PCB could intercalate completely between two base pairs, preferably between Guanine:Cytosine pairs.

Ab initio calculation of intermolecular dispersion energy and induction energy of nitramide dimer

AbstractThe dispersion energies, induction energies and their exchange counterparts (exchange‐dispersion and exchange‐induction energies) between two interacting nitramide molecules at several separations are derived based upon symmetry‐adapted perturbation theory (SAPT). The results show that (1) the effect of intramonomer electron correlation on dispersion energies and induction energies for nitramide dimer system is remarkable especially in the region near the van der Waals minimum distance (0.42 nm). (2) At smaller separations the dispersion energies and the induction energies are largely quenched by their exchange counterparts, and this case in induction interaction is much more remarkable than in dispersion interaction. (3) Since at shorter distances there exists the strong short‐range interaction due to electron transfer which quickly decays and even disappears at larger separations, the two different R‐dependency formulae of induction energies were found: one is cu. R−12.7 at short distances, and the other cu R−7.0 at large separations. The latter R‐dependency is similar to that (ca. R−7.2) of dispersion. (4) In the case of strong polar interaction existing in nitramide dimer, the “true” induction correlation terms of higher order than 1Eind(22) may be important.

Atomic representation of the dispersion interaction energy

A method is presented for dividing the intermolecular dispersion energy into intersite ‘atomic’ contributions. The dispersion energy and the multipole approximation to it are calculated for a series of atom (He,Ne,Ar)–linear molecule (N2, CO, CO2) systems. Damping functions which correct for the multipole approximation are found to be more isotropic for the ‘atomic’ components of the dispersion energy than for the total intermolecular dispersion energy, making the proposed method useful for modelling the dispersion energy. Applications of the method to larger molecules are considered.

Intermolecular dispersion energies from time-dependent density functional theory

Non-expanded dispersion energies are calculated from time-dependent coupled-perturbed density functional theory (DFT) employing various non-hybrid and hybrid exchange-correlation potentials and suitable adiabatic local density approximations for the exchange-correlation kernel. Considering the dimer systems He 2, Ne 2, Ar 2, NeAr, NeHF, ArHF, (H 2) 2, (HF) 2, and (H 2O) 2 it is shown that the effects of intramonomer electron correlation on the dispersion energy are accurately reproduced with the PBE0AC exchange-correlation potential. In contrast, the uncoupled sum-over-states approximation yields inacceptable errors. These are mainly due to neglect of the Coulomb and exchange-correlation kernels and therefore, not substantially improved through an asymptotic correction of the exchange-correlation potential.

The Nature of Protonated Decamethylsilicocene, (Me5C5)2Si+H

Structure and bonding in several stereoisomers of the recently synthesized silyl cation (Me5C5)2Si+H (2) and its hydrogen-substituted analogue (C5H5)2Si+H (3) has been investigated by quantum-mechanical methods. DFT calculations at the B3LYP/6-311G(2d,p)//B3LYP/6-31G(d)+ΔZPVE level as well as coupled cluster calculations at the CCSD(T)/6-311G(d) level for the parent silyl cation 3 reveal that the η1.5:η1.5-coordinated isomer 3c of C2 symmetry is the most stable isomer. Two isomers of 3, the η2:η3-bonded 3f (Cs symmetry) and the η2:η2-coordinated 3e (C2v symmetry), are, however, very close in energy (ΔE < 1 kcal mol-1). This implies that 3 is a highly fluxional molecule which undergoes a series of effectively barrierless haptotropic shifts leading to a circumambulatory migration of the SiH group about the cyclopentadienyl ring. The positive charge in the silyl cation 3 is effectively transferred to the attached cyclopentadienyl substituent, leading to an exceptional thermodynamic stability: the secondary cation 3 is more stable than Me3Si+ by 18.7 kcal mol-1 (at B3LYP/6-311G(2d,p)//B3LYP/6-31G(d)+ΔZPVE). Similarly, for the experimentally observed permethylated silyl cation 2, three low-energy isomers with different hapticities for the silicon have been found to be very close in energy (ΔE < 1.5 kcal mol-1 at B3LYP/6-311G(2d,p)//B3LYP/6-31G(d)), with the η2:η3 isomer 2f only marginally favored. This clearly indicates that also 2 is a highly fluxional molecule. 29Si NMR chemical shift calculations at the GIAO/B3LYP/6-311G(2d,p)//B3LYP/6-31G(d) level suggest that the experimentally observed cation adopts the η3:η2-bonded structure 2f. The unique intramolecular stabilization of the silyl cation 2 by the pentamethylcyclopentadienyl substituents and the additional steric protection of 2 by the methyl groups results in very low association energies AE between the cation and solvent molecules (benzene, AE = −3.2 kcal mol-1; dimethyl ether, AE = −6.4 kcal mol-1). Although these interaction energies must be corrected by ca. −2 kcal mol-1 due to the neglect of intermolecular dispersion energy contributions by the applied DFT method, it can be concluded that 2 is best regarded as a free silyl cation even in solvents as nucleophilic as THF.

Ganglioside GD3 lactones: polar head group-mediated control of the intermolecular organization

The individual properties and intermolecular organization of ganglioside GD3 and of two of its lactone forms (GD3Lactone I and GD3Lactone II) were studied in lipid monolayers. The formation of the first lactone ring in GD3Lactone I eliminates one negative charge and leads to a decrease of the molecular area at all surface pressures. The intermolecular dispersion energy and collapse pressure are higher in GD3Lactone I compared to those in the parent GD3. The surface potential per unit of molecular surface density and the resultant molecular dipole moment are increased in GD3Lactone I with respect to those in GD3 at comparable values of molecular area. In GD3Lactone I the molecular parameters suggest an oligosaccharide chain oriented similarly to that of GD3. On the average, this is perpendicular to the surface, and the resultant polar head-group dipole moment points away from the interface. In GD3Lactone II the negative charges are eliminated, resulting in considerably larger molecular areas than for GD3 and GD3Lactone I at all pressures. The intermolecular dispersion energy of GD3Lactone II is also greatly diminished and the collapse pressure is further increased compared to those of GD3Lactone I. However, the surface potential per unit molecular surface density and the resultant molecular dipole moment of GD3Lactone II are higher than in GD3 Lactone I at similar values of molecular areas. This is probably due to a positive polar head-group dipole moment contribution induced by the additional lactone ring in GD3Lactone II. These changes result from a distorted conformation of the oligosaccharide chain owing to the presence of fused carbohydrate rings which require a greater intermolecular spacing compared to GD3 and GD3Lactone I.

Time-dependent Hartree-Fock calculations of dispersion energy

A new method of computing intermolecular dispersion energies, starting from the SCF wavefunctions of the separate systems, is discussed and illustrated. The method is based on the use of generalized frequency-dependent polarizabilities, calculated using TDHF (time-dependent Hartree-Fock) theory, and all ‘self-consistency’ effects are thus accounted for in the final expressions for the dispersion energy. No multipole expansions are required. The method is shown to be computationally efficient in test calculations of the dispersion interactions between helium atoms and between hydrogen fluoride molecules.

Possible artifacts occurring in the calculation of intermolecular energies from delocalized pictures

The intermolecular energy between two identical subsystems may be calculated from symmetrydelocalized MO's resulting for instance from a preliminary SCF calculation of the supersystem. Then each second-order energy correction mixes intramolecular correlation,R −6 intermolecular dispersion energy, andR −3 components. TheR −3 components disappear through subtle cancellations. The shifted Epstein-Nesbet energy denominators introduce an artificial second-order intermolecularR −1 component, which would be cancelled by off-diagonal third-order terms, as well as a bad asymptotic limit at infinite distances. TheR −1 artifact will also occur in strong symmetrical chemical bonds calculated in the Epstein-Nesbet perturbation scheme from delocalized MO's. These defects will occur in all variational approximate CI techniques which neglect off-diagonal elements between delocalized doubly excited determinants. These artifacts are avoided when using the Moller-Plesset definition of the zeroth order Hamiltonian or when starting from (SCF)localized MO's (even in the Epstein-Nesbet perturbation). The discussion is exemplified on an accurateab initio calculation of the Ar2 molecule.

On the molecular polarizabiltties and intermolecular dispersion energies of deuterated hydrocarbons and related compounds

An effort has been made to discuss the effect of replacing hydrogen by deuterium on electronic polarizabilities and intermolecular dispersion energies of sixteen organic compounds. Standard one-dimensional delta-potential function model of chemical binding has been used. It has been found that the model is capable enough to account for major electronic changes of (C−H) bond region in the form of probability amplitudes of electrons so as to explain H/D isotope effect on the polarizabilities (α M ) and intermolecular dispersion energies (E d).