Electronic Spatial Extent Research Articles

Modelling natural dye molecules lawsone and purpurin in different solvents for DSSC applications: a DFT and TD-DFT study

ABSTRACT The solvent effect on the molecular properties of lawsone and purpurin molecules has been investigated using DFT and TD-DFT. The calculations have been performed using CAM-B3LYP functional and 6-311++G(d,p) basis set. Molecular properties including solute energy, electronic spatial extent, HOMO–LUMO energy gap, thermodynamic properties, the free energy of solvation, electronic properties and UV–visible spectra have been studied. These properties have been analysed in 12 solvents, i.e. benzene, chloroform, aniline, dichloromethane, dichloroethane, benzyl alcohol, 3-pentanone, acetone, ethanol, methanol, acetonitrile and DMSO, and the variation of molecular properties has been studied as a function of the dielectric constant of solvents. We also studied the light-harvesting efficiency (LHE) and the lifetime of excitation of dye molecules in the presence of selected solvents to identify its use as a sensitizer in dye-sensitised solar cells. It has been found that purpurin molecule exhibits a higher LHE and lower excited state lifetime than lawsone molecule. We also observed that the LHE of lawsone molecule has a maximum value for aniline and benzyl alcohol solvents, whereas for purpurin molecule, aniline shows greater LHE values due to the auxochrome effect.

Complex formation of titanocene dichloride anticancer and Al12N12 nano-cluster: A quantum chemical investigation of solvent, temperature and pressure effects

This study investigated the interaction between Al12N12 nano-cluster and titanocene dichloride anticancer drug complex using B3P86 functional in gas and solution phases. Non-covalent interaction (NCI) analysis of this complex was employed for illustration of the Cl⋯Al weak non-covalent interaction. The self-consistent reaction field theory (SCRF) based on the Polarizable Continuum Model (PCM) was applied for testing the solvent effects. The solvent effect on the interaction energy, dipole moment, frontier orbital energy, and global reactivity parameters was examined as well. The changes in the dipole moment, polarizability and electronic spatial extent (ESE) with solvent polarity were analyzed by applying different solvent polarity parameters based on Lippert-Mataga, Bakhshiev and Bilot-Kawski models. In addition, temperature and pressure effects on the thermodynamic parameters of this interaction were illustrated.

Computational Investigation of Interaction of Titanocene Dichloride Anti-Cancer Drug with Carbon Nanotube in the Presence of External Electric Field

In this work, the interaction between titanocene dichloride, an anticancer drug, and carbon nanotube was studied at the B3LYP-D3/6-311G(d,p) level of theory. The external electric field effects on the total energy, dipole moment, electronic spatial extent (ESE), and the HOMO-LUMO gap of the Cp2TiCl2…nanotube molecule were studied. Also, the interaction energy values of the titanocene dichloride with carbon nanotube were calculated. We found good linear relationships between interaction energy, dipole moment, and ESE with external electric field strength.

Quantum‐chemical investigation of the phosphine ligand effects on the structure and electronic properties of a rhenabenzyne complex

AbstractThis study examined the effects of phosphine ligand on the structure and electronic properties of (C5H4)Re(PX3)3Cl rhenabenzyne complexes (X = H, F, Cl, Me) using the hybrid density functional MPW1PW91. Variations in the structure, dipole moment, electronic spatial extent (ESE), and aromaticity of the title complex were studied. In addition, adiabatic and vertical ionization potential and electron affinity values of these complexes were calculated. Correlations between the calculated parameters and Tolman cone angles (θ), Tolman's Electronic Parameter (TEP), as well as the Crabtree's DFT Electronic Parameter (CEP) of the phosphine ligands were illustrated. The para‐delocalization index (PDI) was used to investigate aromaticity in these systems. Natural bond orbital analysis (NBO) was employed for a comprehensive insight into the nature of the bonds in these complexes.

INVESTIGATING THE EFFECTS OF THE EXTERNAL ELECTRIC FIELD ON OSMABENZYNE IN THE GROUND (S0) AND FIRST EXCITED SINGLET (S1) STATES: INSIGHT INTO STRUCTURES, ENERGY, AND PROPERTIES

In this study, the effects of the external electric field (EEF) on osmabenzyne in the ground (S0) and first excited singlet (S1) states are investigated using the hybrid density functional MPW1PW91. The first singlet excited state is determined by the time-dependent density functional theory. Variations in the structure, dipole moment, electronic spatial extent, and aromaticity of the title complex are compared in the presence and absence of EEF. In addition, rotation constants, electron-donating (ω–) and electron-accepting (ω+) powers are calculated. The para-delocalization index is used to investigate the aromaticity in these systems.

Role of π-electron conjugation in determining the electrical responsive properties of polychlorinated biphenyls: a DFT based computational study

Global reactivity descriptors e.g. average polarizabilty (αav), chemical hardness (η), electrophilicity index (ω) of some donor–acceptor substituted polychlorinated biphenyl (PCBs) i.e. 2,2′,5,5′-tetrachloro-1,1′-biphenyl (PCB-1a), 2,5,2′,5′-Tetrachloro-4′-dimethylamino-biphenyl-4-carbonitrile (PCB-1b), Dimethyl-(2,5,2′,5′-tetrachloro-4′-nitro-biphenyl-4-yl)-amine (PCB-1c), 3,3′,5,5′-tetrachloro-1,1′-biphenyl (PCB-2a), 3,5,3′,5′-Tetrachloro-4′-dimethylamino-biphenyl-4-carbonitrile (PCB-2b) and Dimethyl-(3,5,3′,5′-tetrachloro-4′-nitro-biphenyl-4-yl)-amine (PCB-2c) were computed along the torsional potential of biphenyl ring. Density functional based hybrid functional CAM-B3LYP with 6-31G(d) basis were used to all the computational study. Out of the six compounds, variation of the global reactivity descriptors e.g. αav, η, ω as a function of torsional angle of biphenyl ring, three compounds are not in conformity with the respective optimum principle i.e. minimum polarizability, maximum hardness and minimum electrophilicity principle. In this present research article, we have raised this issue that apart from electronically stable conformation, localization of π-electron plays a major role in determining the optimum values of global reactivity descriptors, αav, η & ω. On the other hand computation of first average hyper polarizability (βav) as a function of torsional angle shows that the variation of βav are in good agreement with the optical gap as well as electronic spatial extent ( ) of the conformers of all the six compounds.

Investigating the effects of the external electric field on osmabenzyne in the ground (S0) and first excited singlet (S1) states: Insight into structures, energy, and properties

In this study, the effects of the external electric field (EEF) on osmabenzyne in the ground (S0) and first excited singlet (S1) states are investigated using the hybrid density functional MPW1PW91. The first singlet excited state is determined by the time-dependent density functional theory. Variations in the structure, dipole moment, electronic spatial extent, and aromaticity of the title complex are compared in the presence and absence of EEF. In addition, rotation constants, electron-donating (ω–) and electron-accepting (ω+) powers are calculated. The para-delocalization index is used to investigate the aromaticity in these systems.

The interaction of 5-fluorouracil with graphene in presence of external electric field: a theoretical investigation

In current research, the interaction between 5-fluorouracil (FU), as an anticancer drug, and graphene was studied in the M062X/6-311G(d,p) level of theory. The external electric field effects on the total energy, dipole moment, the energies corresponding to frontier orbitals and HOMO–LUMO gap of the fluorouracil···graphene molecule. Furthermore, the analysis of interaction of the 5-FU with graphene was carried out through the energy decomposition analysis (EDA). There were excellent linear relationships between electronic spatial extent (ESE), frontier orbital energies and energy of interaction with external electric field strength.

Comparison Study on the Prediction of Multiple Molecular Properties by Various Neural Networks

Various neural networks, including a single layer neural network (SLNN), a deep neural network (DNN) with multilayers, and a convolution neural network (CNN) have been developed and investigated to predict multiple molecular properties simultaneously. The data set of this work contains∼134 kilo molecules and their 15 properties (including rotational constant A, B, and C, dipole moment, isotropic polarizability, energy of HOMO, energy of LUMO, HOMO-LUMO gap energy, electronic spatial extent, zero point vibrational energy, internal energy at 0 K, internal energy at 298.15 K, enthalpy at 298.15 K, free energy at 298.15 K, and heat capacity at 298.15 K) at the hybrid density functional theory (DFT) level from the QM9 database. Coulomb matrix (CM) converted from the database representing every molecule uniquely and its eigenvalue are respectively used as the input of machine learning. The accuracies of predictions have been compared among SLNN, DNN and CNN by analyzing their mean absolute errors (MAEs). Using eigenvalues as input, both SLNN and DNN can give higher accuracy for the prediction of specific energy properties ( U0, U, H, and G). For the prediction of all 15 molecular properties at a time, DNN with a 3-layers network exhibits the best results using the full CM as input. The number of layers in DNN play a key role in the prediction of multiple molecular properties simultaneously. This work may provide possibility and guidance for the selection of different neural networks and input data forms for prediction and validation of multiple parameters according to different needs.

Analysis of the Interaction Between the C20 Cage and cis-Ptcl2(NH3)2: A DFT Investigation of the Solvent Effect, Structures, Properties, and Topologies

This study investigates the interaction between C20 and the cis-PtCl2(NH3)2 complex using MPW1PW91 quantum chemical calculations in gas and solution phases. Two interaction modes between C20 and the cis-PtCl2(NH3)2 complex are considered: I-isomer (η2-C20) and II-isomer (η1-C20). It also determines the effects of the solvent polarity on the dipole moment, electronic spatial extent (ESE), structural parameters, and frontier orbital energies of two possible isomers of the C20…cis-PtCl2(NH3)2 complex. The bonding interaction between C20 and the cis-PtCl2(NH3)2 complex was examined through energy decomposition analysis (EDA). The metal–ligand bonds are evaluated using the percentage composition of the specific groups of frontier orbitals. The quantum theory of atoms in molecules (QTAIM) analysis is applied to assess the Pt–C bonds within the complex. Finally, the Pt–C spin-spin coupling constants are calculated using the gauge independent atomic orbital (GIAO) method.

Design of a Novel Series of Donor-Acceptor Frameworks via Superalkali-Superhalogen Assemblage to Improve the Nonlinear Optical Responses.

Presently, many researches are directed toward the design of novel superatoms with high nonlinear optical responses. Inspired by a fascinating finding of superatoms which were designed by bonding superhalogen (Al13 nanocluster) with superalkalis (M3O, M = Na and K), we suggest an effective strategy to form a series of typical donor-acceptor frameworks with high nonlinear optical responses via bonding the superalkalis M3O (Li3O, Na3O, K3O, Li2NaO, Li2KO, Na2LiO, Na2KO, K2LiO, K2NaO, and LiNaKO) with low ionization potential to the superhalogen Al13 with large electron affinity. The ionization potential, electronic spatial extent, electric field gradient tensors of 17O nuclei, and natural bond orbital charge values of the superalkalis M3O were also calculated. We found that the M ligands have the remarkable effect on the ionization potential as well as 17O nuclear quadrupole resonance parameters of the superalkalis M3O. Our results also represented that the bonding superalkalis can efficiently narrow wide HOMO-LUMO gap and considerably enhance first hyperpolarizability of the pristine Al13, due to electron transfer in this type of superatom. Also, the effect of oriented external electric fields on the nonlinear optical responses of the superatoms M3O-Al13 has been systematically explored. We found that the first hyperpolarizability of the superatom compounds can be gradually increased by increasing the imposed oriented external electric field from zero to the critical external electric field along the charge transfer direction (M3O → Al13). In this respect, this work reveals an effective approach to gradually enhance the nonlinear optical responses of the superatoms through applying oriented external electric fields.

Effect of chain length and donor–acceptor substitution on the electrical responsive properties of conjugated biphenyls: a DFT-based computational study

ABSTRACTThe effect of donor–acceptor (D-A) substituent and chain length on the electrical polarisabilities and first hyper polarisability of cis and trans biphenyl oligomeric compounds have been investigated using density functional theory-based hybrid functional CAM-B3LYP with 6-311G (2d,2p) basis set. Our extensive computational study reveals that both average polarisability and first hyper polarisability of the studied compounds increase with the increasing ethylene spacer chain length. Again the substitution of donor (NMe2) and acceptor (C≡N) at the para position of the phenyl rings to each oligomer shows order of magnitude increase of both αav and βav value compared to the unsubstituted one. This increased αav and βav values have been explained due to increasing charge transfer contribution resulting from decreasing optical energy gap (ΔE = S1 − S0) upon D-A substitution. It is also observed that the charge transfer contribution to first hyperpolarisability (βCT) is more than the polarisability (αCT) for the studied molecules. The electronic spatial extent (<R2>) which is a measure of electron density volume around the molecule is found to play a major role along with the intramolecular charge transfer character to explain the non-linear variation of first hyperpolarisability (βav) as a function of ethylene spacer chain length (n) and D-A substitution.

Methoxymethane C-O Bond Strengths: Do Their Changes Result from Hyperconjugation or Polar Effects?

The methoxymethanes have been studied and compared with the fluoromethanes. The energies and atomic charges were calculated using MP2/aug-cc-pVTZ, and the group separation energies and bond dissociation enthalpies were calculated using CBS-QB3. The group separation energies are endothermic and the BDE increases with additional substitution as a result of the increase in charge at the central carbon. The greater charge leads to a stronger bond to the new substituent as well as to the original substituents. With the methoxymethanes, there is a linear relationship between the BDE and the atomic charge at C. The energies of the several methoxymethane conformers were calculated, and their energies usually increase with increasing values of the electronic spatial extent in accord with a proposal by Gillespie. The role of hyperconjugation in these cases is not settled.

Prediction Errors of Molecular Machine Learning Models Lower than Hybrid DFT Error

We investigate the impact of choosing regressors and molecular representations for the construction of fast machine learning (ML) models of 13 electronic ground-state properties of organic molecules. The performance of each regressor/representation/property combination is assessed using learning curves which report out-of-sample errors as a function of training set size with up to ∼118k distinct molecules. Molecular structures and properties at the hybrid density functional theory (DFT) level of theory come from the QM9 database [ Ramakrishnan et al. Sci. Data 2014 , 1 , 140022 ] and include enthalpies and free energies of atomization, HOMO/LUMO energies and gap, dipole moment, polarizability, zero point vibrational energy, heat capacity, and the highest fundamental vibrational frequency. Various molecular representations have been studied (Coulomb matrix, bag of bonds, BAML and ECFP4, molecular graphs (MG)), as well as newly developed distribution based variants including histograms of distances (HD), angles (HDA/MARAD), and dihedrals (HDAD). Regressors include linear models (Bayesian ridge regression (BR) and linear regression with elastic net regularization (EN)), random forest (RF), kernel ridge regression (KRR), and two types of neural networks, graph convolutions (GC) and gated graph networks (GG). Out-of sample errors are strongly dependent on the choice of representation and regressor and molecular property. Electronic properties are typically best accounted for by MG and GC, while energetic properties are better described by HDAD and KRR. The specific combinations with the lowest out-of-sample errors in the ∼118k training set size limit are (free) energies and enthalpies of atomization (HDAD/KRR), HOMO/LUMO eigenvalue and gap (MG/GC), dipole moment (MG/GC), static polarizability (MG/GG), zero point vibrational energy (HDAD/KRR), heat capacity at room temperature (HDAD/KRR), and highest fundamental vibrational frequency (BAML/RF). We present numerical evidence that ML model predictions deviate from DFT (B3LYP) less than DFT (B3LYP) deviates from experiment for all properties. Furthermore, out-of-sample prediction errors with respect to hybrid DFT reference are on par with, or close to, chemical accuracy. The results suggest that ML models could be more accurate than hybrid DFT if explicitly electron correlated quantum (or experimental) data were available.

A structure-property interplay between the width and height of cages and the static third order nonlinear optical responses for fullerenes: applying gamma density analysis.

To reveal a new structure-property relationship regarding the nonlinear optical (NLO) properties of fullerenes that are associated with gamma (γ) density, fullerenes I (C40, C50, C60 and C70), whose heights range from 4.83 to 7.96 Å, and II (C24, C36, C48 and C72), whose widths range from 4.45 to 8.22 Å, have been the research objects. Calculation of their geometric and electronic structures, absorption spectra, and the second hyperpolarizability (γ) and the γ density analysis have been performed. It is found that the electronic spatial extent and the polarizability (α) value increase linearly as the fullerenes increase by every 12 carbon atoms. Similarly, the γ values are also proportional to the fullerene size. It is worth noting that the relative magnitude of γxxxx and γzzzz was exactly consistent with that of the width and height of fullerenes. The analysis of γ density provides the essential reason for this result, that is, the magnitude of the contribution to γ values associated with γ densities is proportional to the density amplitudes multiplied by the distance between them. Larger fullerenes possess larger density amplitudes and longer distances, resulting in larger γ values with respect to smaller fullerenes. This work presents a new structure-property interplay between the width and height of the fullerenes and their second hyperpolarizability γ. Moreover, the γ density analysis provides a new insight to explore the nature of the relationship between the structure and the NLO properties.

How different is pyrimidine as a core component of DNA base from its diazine isomers: A DFT study?

AbstractRecent photoemission spectroscopic (X‐ray photoemission spectra) study revealed less dramatic chemical changes for pyrimidine (PyM, 1, 3‐diazine) with in its ionization potential. Present systematic study using density functional theory calculations shows that PyM is indeed quite different from its diazine isomers (PyD, 1, 2‐diazine and PyA, 1, 4‐diazine). It is discovered that the most stable isomer PyM is relaxed from C2V to C1 point symmetry with a total electronic energy deduction of −15.86 kcal.mol−1. Although not substantial, PyM has the smallest molecule shape (electronic spatial extent) and the largest HOMO‐LUMO energy gap of 5.65 eV; only one absorption band in the region of 200–300 nm of the UV‐Vis spectrum but three clusters of chemical shift in the carbon and hydrogen NMR spectra. The energy decomposition analyses revealed that the interaction energy (ΔEInt) of PyM is preferred over PyA by 4.08 kcal.mol−1 and over PyD by 22.32 kcal.mol−1, with the preferred NCN bond revealed by graph theory.

Effect of π-conjugate units on the ferrocene-based complexes: Switchable second order nonlinear optics controlled by redox stimuli

The control of rotational motion, using an external impulse (such as redox), has been intensively pursued as nonlinear optics switch. Four redox responsive ferrocene-based actuators with varied π-conjugated units have been systematically investigated by the density functional theory. The open structures of these complexes with antiparallel orientation of both π-conjugated units are due to the large charge repulsion effect, while the closed forms are stabilized by the intramolecular π–π stacking interactions.The rotational motion can be triggered by reduction process preferentially centered on the π-conjugated units. The polarizabilities and first hyperpolarizabilities of complexes [3]closed2+ and [4]closed2+ are significant enhanced, which are respectively related to the electronic spatial extent and intramolecular interlayer charge transfer occurred between two respective π-conjugated units. Overall, the present work shows that one can design the molecular nonlinear optical switches characterized by a large contrast varying from zero to a large value along the reversible transformations.

Theoretical study of valence orbital response to guanine tautomerization in coordinate and momentum spaces

The binding energy spectra and electron momentum spectra of eight stable guanine tautomers are calculated in the complete valence space. The present results show that the canonical keto (C=O) guanine N(9)H tautomer (GU1) possesses the largest dipole moment, molecular electronic spatial extent, molecular hardness value, and the minimum first vertical ionization potential (VIP). Valence orbital profile investigations find that several orbitals remain almost unchanged during tautomerization, such as frontier highest occupied molecular orbital 39a and 18a. Several orbitals with interchanged order and inverse direction in charge spatial orientations are also detected. Outer valence orbitals (with smaller VIPs) show more complex orbital shapes in the momentum space than those of inner ones (larger VIPs) due mainly to the relatively strong inter-orbital interaction and delocalized electronic distributions. Proton rotation along C–O(H) and C–N(H) axes within hexagonal ring causes smaller influence to orbital profiles than those of proton migration within pentagonal and/or hexagonal rings. Orbital variation trends between enol (GU3–GU5) and keto (GU1, GU2, GU6–GU8) tautomers are observed, including the signature orbitals of enol form, the variation tendency of total orbital intensity, and the variation order of the maximum orbital intensity. In the outer valence momentum space (outside 26a), orbital composed by pz electrons show single peak with a gradual increasing peak site from 0.5 a.u. of inner valence orbital to 1.0 a.u. of outer valence orbital, whereas orbitals composed by px,y electrons form double peaks with respective sites at about 0.5 and 1.5 a.u., only three px,y-orbitals present single peaks (33a,34a,36a). The general variation trends in the complete valence space for all the valence orbitals on their intensities, peak sites, and orbital components are concluded.

THEORETICAL STUDY OF MAGNETIC SUSCEPTIBILITY AND OPTICAL ACTIVITY OF SMALL MOLECULES CONTAINING ONE CHIRAL CENTER

In the first part of this work, correlation between optical activity and elements of magnetic susceptibility tensor (MST) for five classes of model small molecules containing a single chiral center has been studied using quantum computational techniques at DFT-B3LYP level of theory with 6-311G basis set. Several molecular properties are used to reduce the MST elements prior to the examination of the correlation. This study showed a close correlation between optical activity and the off-diagonal MST elements reduced by the electronic spatial extent . In the second part of this work, effects of the type of substitutions and their distances from the chiral center on the optical activity of these molecules have been investigated. Results of this work show that optical activity is reduced effectively upon distancing the substitution groups from the chiral center. Furthermore, the set of substitutions with higher electron densities and larger differences in their electronic structures result in higher optical activity.

Effect of electronic spatial extents (ESE) of ions on overpotential of lithium ion capacitors

The electronic spatial extent (ESE) of ions was defined as a major concept for assessing the cause of overpotential in the charging and discharging processes of a nanoporous activated carbon (AC) electrode. The performance degradation of AC/Li half-cells was caused by the overpotential, which was in discord with the electrolyte conductivity and ion size. Compared to the overpotential with the salt concentration, the AC/Li half-cell with a high concentration had a smaller overpotential, and its discharge patterns were similar to the curves obtained from the half-cells with a smaller ESE of BF4− ion. The ESE is a more realistic solution for determining the overpotential of the nanoporous capacitor, such as supercapacitor and Li ion capacitor, because its capacity is dependent on the electron density at the electric double layer of the capacitor electrode.