Calculation Of Molecular Polarizabilities Research Articles

Data-driven tailoring of molecular dipole polarizability and frontier orbital energies in chemical compound space.

Understanding correlations - or lack thereof - between molecular properties is crucial for enabling fast and accurate molecular design strategies. In this contribution, we explore the relation between two key quantities describing the electronic structure and chemical properties of molecular systems: the energy gap between the frontier orbitals and the dipole polarizability. Based on the recently introduced QM7-X dataset, augmented with accurate molecular polarizability calculations as well as analysis of functional group compositions, we show that polarizability and HOMO-LUMO gap are uncorrelated when considering sufficiently extended subsets of the chemical compound space. The relation between these two properties is further analyzed on specific examples of molecules with similar composition as well as homooligomers. Remarkably, the freedom brought by the lack of correlation between molecular polarizability and HOMO-LUMO gap enables the design of novel materials, as we demonstrate on the example of organic photodetector candidates.

Growth, structural, optical, Z-scan and dielectric analysis of 2-Amino-4-methylpyridinium 2-chloro 4-nitro benzoate crystals for third order non-linear optical applications

• AMPCNB was synthesized and grown as crystal by slow evaporation method. The centrosymmetric space group of AMPCNB was concluded as P21/n. • The lower cut-off wavelength of AMPCNB was found to be 318 nm and band gap energy gap was 3.16 eV. • The NLO parameters, refractive index (n2) = 5.610 × 10−8 cm2/W and absorption coefficient = 0.033 × 10−4 cm/W were found. • The dielectric study reveals the phase transition at high temperature. An organic nonlinear optical material 2-Amino-4-methylpyridinium 2-chloro 4-nitro benzoate (AMPCNB) was synthesized and large size single crystals were grown by slow evaporation solution growth method. Single crystal X-ray diffraction study showed that the title compound belongs to monoclinic crystal system with P2 1 /n space group. In the title molecular salt, C 6 H 9 N 2 + ·C 7 H 3 ClNO 4 − , the original pyridine N atom of 2-amino-4-methylpyridine is protonated. The chloro and the carboxylic acid group of nitrobenzoic acid is deprotonated. In the crystal, the protonated N atom and the 2-amino group of the cation are hydrogen bonded to the carboxylate O atoms of the anion via a pair of N-H···O hydrogen bonds, forming a R 2 2 (8) ring motif. The ion pairs are further connected via N-H···O and C-H···O hydrogen bonds. The molecules are further stabilized by C-H···π and π-π interactions. The UV–VIS-NIR study was performed to investigate the transparency window and lower cutoff wavelength of the compound. The third harmonic efficiency of title compound has been studied using Z-scan technique using continuous wave Nd:YAG laser to confirm its saturable absorption and self-defocusing effect. Theoretical calculation of molecular polarizability, which is helpful in device fabrication, was carried out from Penn gap, Clausius-Mossotti equations and the obtained results were compared. The Vickers’ micro hardness test was carried out at room temperature and obtained results were investigated using classical Meyer's law.

Property-optimized Gaussian basis sets for lanthanides

Property-optimized Gaussian basis sets of split-valence, triple-zeta valence, and quadruple-zeta valence quality are developed for the lanthanides Ce-Lu for use with small-core relativistic effective core potentials. They are constructed in a systematic fashion by augmenting def2 orbital basis sets with diffuse basis functions and minimizing negative static isotropic polarizabilities of lanthanide atoms with respect to basis set exponents within the unrestricted Hartree-Fock method. The basis set quality is assessed using a test set of 70 molecules containing the lanthanides in their common oxidation states and f electron occupations. 5d orbital occupation turns out to be the determining factor for the basis set convergence of polarizabilities in lanthanide atoms and the molecular test set. Therefore, two series of property-optimized basis sets are defined. The augmented def2-SVPD, def2-TZVPPD, and def2-QZVPPD basis sets balance the accuracy of polarizabilities across lanthanide oxidation states. The relative errors in atomic and molecular polarizability calculations are ≤8% for augmented split-valence basis sets, ≤ 2.5% for augmented triple-zeta valence basis sets, and ≤1% for augmented quadruple-zeta valence basis sets. In addition, extended def2-TZVPPDD and def2-QZVPPDD are provided for accurate calculations of lanthanide atoms and neutral clusters. The property-optimized basis sets developed in this work are shown to accurately reproduce electronic absorption spectra of a series of LnCp3 '- complexes (Cp' = C5H4SiMe3, Ln = Ce-Nd, Sm) with time-dependent density functional theory.

Molecular Polarizabilities in Aqueous Systems from First-Principles.

We discuss the results of first-principles calculations of molecular polarizabilities in condensed systems composed of well-defined building blocks, with a focus on water and simple aqueous solutions. We show that molecular polarizabilities are subtle fingerprints of structural changes induced in liquid water by the environment, e.g., the presence of ions and confined media, as well as by temperature and pressure. We also point out the importance of molecular polarizabilities in the calculation and interpretation of specific vibrational signatures of aqueous systems, notably Raman and sum-frequency generation spectra.

Synthesis and Controllable Growth Dynamics of Third Order Nonlinear Optical Material of 2-Amino-4-Methylpyridinium 2-Chloro 4-Nitro Benzoate Electro-Mechanical Investigation and Device Fabrication

An organic nonlinear optical material 2-Amino-4-methylpyridinium 2-chloro 4-nitro benzoate (AMPCNB) was synthesized and large size single crystals were grown by slow evaporation solution growth method. Single crystal X-ray diffraction study showed that the title compound belongs to monoclinic crystal system with P21/n space group. A powder XRD study was performed to ascertain its phase. The UV–VIS-NIR study was performed to investigate the transparency window and lower cutoff wavelength of the compound, no absorption has been observed between 318 and 1100 nm. The third harmonic efficiency of the title compound has been studied using the Z-scan technique using continuous-wave Nd:YAG laser to confirm its saturable absorption and self-defocusing effect. The photo conducting and charge transport properties are analyzed using photoconductivity and dielectric measurements. Theoretical calculation of molecular polarizability, which is helpful in device fabrication, was carried out from Penn gap, Clausius-Mosotti equations and the obtained results were compared. Mechanical properties of the grown crystal were investigated by Vicker’s microhardness study.

Assessment of the proposed pseudo-potential theoretical model for the static and dynamic Raman scattering intensities: Multivariate statistical approach to quantum-chemistry protocols.

Accurate calculation of molecular polarizabilities and Raman intensities required high-level correlated wave functions (CCSD) and large basis set with the inclusion of electronic correlation within experimental precision. These requirements, in terms of time and computation, are economically costly. Polarized Gaussian basis sets adapted to effective core potentials (ECPs) for the static and frequency dependent Raman intensities is presented. The results of the proposed basis sets at CCSD and DFT levels in comparison with Sadlej-pVTZ, as reference basis set, show quite a good quantitative agreement in the properties with a valuable reduction in the computational time and resources. Multivariate principal component analysis (PCA) was performed to study the assessment of the efficiency of proposed methodology and diagnose the inherent information related to the kind of normal vibrational mode of each molecule, based on the variations in the computed Raman intensities. The results, in the form of score-plots, explored a clear segregation and classification among the Raman intensities data, revealing its dependence on the excitation frequencies of laser and nature of the vibrational mode of each molecule of interest. Moreover, the projection of the loadings-plots of the PCs successfully enabled to classify the most correlated computational methods in to the same groups, and made isolations of the less efficient basis functions at the corresponding theoretical method.

Bond-Dependent Thole Model for Polarizability and Spectroscopy.

We present a new model for the calculation of molecular polarizabilities from effective atomic polarizabilities. This model is based on the Thole modified dipole interaction model for molecular polarizabilities, where the total polarizability is computed as a sum of effective atomic polarizabilities modified by dipole-dipole interactions. We extend this model by making the atomic polarizabilities explicit functions of the interatomic distances, scaling them by the radius of the volume an atom occupies in a molecule. We use the SCAN functional to show that this model, denoted TholeL, yields accurate molecular polarizabilities with little dependence on the training set. We also demonstrate that the TholeL model yields accurate polarizabilities for configurations far from the ground state structure for a wide range of molecules. Finally, we show that the TholeL model can be used to generate accurate Raman spectra for water, crystalline urea, and urea in water from ab initio molecular dynamics simulations.

Evaluation of free volume and anisotropic chain orientation of Tröger's base (TB)-based microporous polyimide/copolyimide membranes

Polarization-dependent refractive indices were utilized to probe the free volume and anisotropic chain orientation of several types of microporous polyimides (PIs)/copolyimides (co-PIs) based on Tröger's base (TB). The properties related to the free volume and chain orientation, such as dielectric constants and linear thermal expansion behaviors, as well as the out-of-plane thermal diffusivity (D⊥), were quantitatively investigated. The free volume fractions (Vf) of 0.183–0.228 were estimated for the membranes based on the Lorentz-Lorenz equation and molecular polarizability calculations. The TB-based PIs/co-PIs exhibited relatively low average refractive indices (1.5208–1.6061), low-to-moderate birefringence (0.0181–0.0505) at 1310 nm, and ultra-low D⊥ values ranging from 6.2 to 9.6 × 10−8 m2/s, depending on the chemical structures and the preparation conditions. Their excellent overall performance suggests their potential applications, for example, in protective sunshades, heat insulation tape, and thermal barrier coatings.

Negative optical anisotropic behaviour of two higher homologues of 5O. m series of liquid crystals

In this paper, we report optical studies of two higher homologous of 5O. m (m=14,16) series which are found to exhibit negative optical anisotropy in our studies. These compounds are calamatic interdigitated with unsymmetrical alkyl chain length. The compounds show high refractive indices in our experiment. The experimentally measured refractive indices data used to calculate the molecular polarizability, order parameter, Lorentz and internal field factors. We observed that, the molecular polarizability of both the sample increases with the increase in temperature. Vuks' and Neugebauer's models are adopted for the calculation of molecular polarizabilities. Direct extrapolation method for birefringence measurements and Vuks', Neugebaur's, modified Vuks' based on Haller's extrapolation methods were used to determine the order parameter of the LC compound. The results from our study show the same nature for both the liquid crystal compounds.

Improving UV stability of tolane-liquid crystals in photonic applications by the ortho fluorine substitution

A series of ortho fluoro-tolane liquid crystals was prepared via multi-step reactions based on 4-alkylcyclohexanecarboxylic acids. Their synthetic routes, thermotropic mesophases and UV stability properties are discussed by comparision with the non-fluorinated analogs. All of the measurements from DSC, UV-vis absorption and fluorescence emission spectra demonstrate that the presence of ortho fluorine can significantly improve the UV stability of tolane-liquid crystals. Meanwhile, the ultimate failure mechanism of tolane-LCs during UV exposure is deduced by a photochemical reaction. DFT calculations of molecular polarizabilities, triple bond lengths, electrostatic potential maps and molecular orbitals are used to correlate the experimental findings. The interaction mechanism for stabilization of the tolane structures by the ortho fluoro substitution is also explained. This work may provide an effective solution for the obstacle existed in tolane-liquid crystals and pave a way for their applications in liquid crystal photonics.

Natural orbital functional calculations of molecular polarizabilities and second hyperpolarizabilities. The hydrogen molecule as a test case

The longitudinal polarizability (α) and second hyperpolarizability (γ) of the H2 molecule as a function of the internuclear distance are calculated using the PNOF5 level of theory. It is shown that PNOF5 gives accurate results for the longitudinal α and γ over the whole curve range, even for those structures exhibiting a high degree of diradical character. The good agreement between these results and reference full-CI data highlights the adequacy of PNOF5 to treat electronic systems exhibiting large static electron correlation and shows a promising accuracy in calculating nonlinear optical properties for systems covering a large range of diradical character. The results further support the paradigm of using molecules with intermediate diradical character to enhance the second hyperpolarizabilities.

Temperature-dependent microwave dielectric relaxation studies of hydrogen bonded polar binary mixtures of propan-1-ol and propionaldehyde

The molecular interaction between the polar systems of propan-1-ol and propionaldehyde for various mole fractions at different temperatures were studied by determining the frequency dependent complex dielectric permittivity by using the open-ended coaxial probe technique method in the microwave frequency range from 20MHz to 20GHz. The geometries are optimized at HF, B3LYP and MP2 with 6-311G and 6-311G+ basis sets. Dipole moments of the binary mixtures are calculated from the dielectric data using Higasi’s method and compared with the theoretical results. Conformational analysis of the formation of hydrogen bond between the propan-1-ol and propionaldehyde is supported by the FT-IR and molecular polarizability calculations. The average relaxation times are calculated from their respective Cole–Cole plots. The activation entropy, activation enthalpy and Kirkwood correlation ‘g’ factor, excess permittivity (εE), excess inverse relaxation time (1/τ)E, Bruggeman parameter (fB) have also been determined for propan-1-ol and propionaldehyde and the results were correlated.

Microwave dielectric relaxation studies of hydrogen bonded polar binary mixtures of isobutanol and aniline

The molecular interaction between the polar systems of isobutanol and aniline for various mole fractions at different temperatures were studied by determining the frequency dependent complex dielectric permittivity by using the open-ended coaxial probe technique method in the microwave frequency range from 20MHz to 20GHz. The geometries are optimized at HF and B3LYP with 6-31G and 6-31G+ basis sets. Dipole moments of the binary mixtures are calculated from the dielectric data using Higasi’s method and compared with the theoretical results. Conformational analysis of the formation of hydrogen bond between the isobutanol and aniline is supported by the FT-IR and molecular polarizability calculations. The average relaxation times are calculated from their respective Cole–Cole plots. The activation entropy, activation enthalpy and Kirkwood correlation ‘g’ factor, excess permittivities (εE), Bruggeman parameters (fB) have also been determined for isobutanol and aniline and the results were correlated.

Basis set independent calculation of molecular polarizabilities

Basis set independent calculation of molecular polarizabilities

An augmented Gaussian basis set for calculations of molecular polarizabilities on platinum compounds

Recently, segmented all-electron contracted double zeta valence plus polarization function (DZP) basis sets for the Pt element were constructed to be used in conjunction with the non-relativistic and Douglas–Kroll–Hess Hamiltonians. In this work, with the purpose of having a better description of electron affinity, polarizabities, and hydrogen bonding, the DZP set was augmented with diffuse (s, p, and d symmetries) and polarization (f symmetry) functions that were optimized for the anion at the Hartree–Fock and Mϕller–Plesset second-order levels, respectively. From optimized relativistic geometries and using non-hybrid and hybrid functionals, the performance of the augmented DZP (ADZP) set is assessed for predicting static electric dipole moment and polarizability of PtH, PtH 2, and antitumor drugs (cisplatin and carboplatin). Despite its compact size, the ADZP set demonstrates consistent, efficient, and reliable performance. ADZP electric property calculations showed to be as fast as those that use augmented effective core potential basis sets.

Assessment of the performace of the functional density theory to compute molecular polarizabilities using molecular polarization maps

In the present report we analyze the performance of DFT to compute molecular polarizabilities through the analysis of molecular polarization potential that can be used as a tool to understand their spatial effects in the calculation of molecular polarizabilities. This is done in the present report through the results obtained for three reference molecules: hydrogen cyanide, formaldehyde and urea. Calculations were carried out at the density functional theory using the BLYP and B3LYP functionals. The results of the polarization maps reveal similar trends observed with the calculation of the different components of the polarizability tensor. However, the use of the maps permits to understand spatial effects specific for each level of calculation and each basis set.

What made possible the accurate calculations of NMR spin–spin coupling constants?

The 1990s were an exciting time at the Quantum Theory Project of the University of Florida, during which several new developments in coupled cluster (CC) theory took place. One in particular is the development of the equation of motion coupled cluster (EOM-CC) method. It was realized that the EOM-CC excited states could be used to compute second-order properties in a sum over state formulation and the benchmark molecular polarizability calculations have since shown that EOM-CC performs remarkably well. The NMR spin–spin coupling is also a second-order property, and thus calculable by the new EOM-CC methodology. It was a common observation of reviews published at the time that a need existed for accurate nuclear magnetic resonance (NMR) indirect spin–spin coupling constants for medium-size molecules. This article is a first-hand account of the development of the EOM-CC methods for NMR spin–spin coupling constants and their successful applications to problems of interest.

Orientational Order Parameter – 1 A Birefringence Study

Many methods are known for the estimation of the orientational order parameter in the nematic phase of a liquid crystal. The order parameter can be calculated directly from a macroscopic quantity measured in the experiment. The birefringence technique has been exploited for the evaluation of order parameter in the nematic phase along with the density measurements which are needed for the calculation of molecular polarizabilities of the molecule. Density and birefringence studies are carried out on four compounds viz., N-(p-n-octyloxybenzylidene)-p-n-propyloxy, butyloxy, hexyloxy and heptyloxy anilines, 8O.O3, 8O.O4, 8O.O6 and 8O.O7. The order parameter is obtained from the molecular polarizabilities obtained using two different internal field models due to Vuks and Neugebauer and the molecular anisotropy calculated using Lippincott δ-function model. The results reveal that both the models agree very near to the isotropic-nematic transition and diverge as nematic field stabilizes. Further, the results are compared with those obtained using Haller's extrapolation technique.

Analysis of the basis set and correlation effects on the computation of molecular polarizabilities using molecular polarization maps

In the present report, we analyze the effect of augmenting the basis set and the level of the theory in the computation of the molecular polarization potential and it is used as a tool to understand their spatial effects in the calculation of molecular polarizabilities. This is analyzed in the present report through the results obtained for three reference molecules: hydrogen cyanide, formaldehyde and urea. Accordingly, different basis sets were used for the calculations, including: 6-31G(D), 6-31G(D,P), 6-31G(2D,2P) and 6-31++G(2D,2P). On the other hand, calculations at different levels of the theory were considered, including: Hartree–Fock, Moller–Plesset second order (MP2) and fourth order (MP4) as well as the functionals BLYP and B3LYP at the density functional theory. The results of the polarization maps reveal similar trends observed with the calculation of the different components of the polarizability tensor. However, the use of the maps permits to understand spatial effects specific for each level of calculation and each basis set.

Auxiliary density perturbation theory

A new approach, named auxiliary density perturbation theory, for the calculation of second energy derivatives is presented. It is based on auxiliary density functional theory in which the Coulomb and exchange-correlation potentials are expressed by auxiliary function densities. Different to conventional coupled perturbed Kohn-Sham equations the perturbed density matrix is obtained noniteratively by solving an inhomogeneous equation system with the dimension of the auxiliary function set used to expand the auxiliary function density. A prototype implementation for the analytic calculation of molecular polarizabilities is presented. It is shown that the polarizabilities obtained with the newly developed auxiliary density perturbation approach match quantitative with the ones from standard density functional theory if augmented auxiliary function sets are used. The computational advantages of auxiliary density perturbation theory are discussed, too.