Validation of semiempirical PM6 method for the prediction of molecular properties of polycyclic aromatic hydrocarbons and fullerenes (original) (raw)
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Correlated Electronic States of a Few Polycyclic Aromatic Hydrocarbons: A Computational Study
Journal of Physical Chemistry A, 2019
In recent years Polycyclic Aromatic Hydrocarbons (PAHs) have been studied for their electronic properties as they are viewed as nanodots of graphene. They have also been of interest as functional molecules for applications such as light emitting diodes and solar cells. Since last few years varying structural and chemical properties corresponding to the size and geometry of these molecules have been studied both theoretically and experimentally. In this paper, we carry out a systematic study of the electronic states of several PAHs using the Pariser-Parr-Pople model which incorporates long-range electron correlations. In all the molecules studied by us, we find that the 2A state is below the 1B state and hence none of them will be fluorescent in the gaseous phase. The singlet-triplet gap is more than one-half of the singlet-singlet gap in all cases and hence none of these PAHs can be candidates for improved solar cell efficiencies in a singlet fission. We discuss in detail the properties of the electronic states which include bond orders and spin densities (in triplets) of these systems.
Journal of Molecular Structure-theochem, 2000
Recently we have shown that it is possible to group and identify the carcinogenic activity of the polycyclic aromatic hydrocarbons (PAHs) using very simple rules derived from simple Hu Èckel calculations. In this work we have carried out similar calculations using semi-empirical methods in order to investigate whether the derived rules are method dependent. We present PM3 (Parametric Method 3) and ZINDO-CI (Zerner Intermediate Neglect of Differential Overlap-Con®guration Interaction) study on the electronic structure of PAHs. Very similar rules, based on the concept of electronic local density of states over speci®c molecular regions, are derived from PM3 calculations showing that they are essentially method independent. The analysis of the ZINDO-CI results for the intensity of the threshold transitions (®rst optical transitions) and the composition of the CI contributions also show a differentiated behavior for the strong carcinogenic molecules and the inactive ones. q
Chemosphere, 2003
Multivariate characterization of 60 polycyclic aromatic hydrocarbons (PAHs) was performed using data from literature and semi-empirical molecular orbital calculations. This dataset was analyzed by principal component analysis and projections to latent structures by means of partial least square. The PAHs were found to distribute in the chemical domain in several groups mainly governed by the number of aromatic rings and the number of five-membered rings. The multivariate model and training set was used to predict GC retention times on a non-polar column (DB-5). Using a 2 4 experimental design on the principal components of the chemical characterization model, a test set of PAHs was selected dependent on the distribution in the chemical domain of the PAHs. Such a test set is expected to improve selection of PAHs for future testing and modeling of both biological and chemical responses. Although the model of GC retention times was good, the precision was however not good enough for practical use.
Validation of PM6 & PM7 semiempirical methods on polarizability calculations
2015
Modern semiempirical methods such as PM6 and PM7 are often used to explore the electronic structure dependent properties of molecules. In this work we report the evaluation of PM6 and PM7 methods towards linear and nonlinear optical polarizability calculations for different molecules and solid nanoclusters. The results are compared with reported experimental results as well as theoretical results from other high level theories for the same systems. It is found that both methods produce accurate results for small molecules and the accuracy increases with the increase in asymmetry of the medium sized organic molecules and accuracy reduces for solid nanoclusters.
Polarized-unpolarized ground state of small polycyclic aromatic hydrocarbons
International Journal of Quantum Chemistry, 2012
Do polyacenes, circumacenes, periacenes, nanographenes and graphene nanoribbons show a spin polarized ground state? In this work, we present mono-determinantal (Hartree-Fock and Density Functional Theory types), and multi-determinantal calculations (Møller-Plesset and Coupled Cluster), for several families of unsaturated organic molecules (n-Acenes, n-Periacenes and n-Circumacenes). All HF calculations and many DFT show a spin-polarized (antiferromagnetic) ground state, in agreement with previous calculations. Nevertheless, the multi-determinantal calculations, carried out with perturbative and variational wavefunctions, show that the more stable state is obtained starting from the unpolarized Hartree-Fock wavefunction. The trend of the stabilisation of wavefunctions (polarized or unpolarized) with respect to exchange and correlation potentials, and to the number of benzene rings, has been analysed. A study of the spin (<Ŝ 2 >) and the spin density on the carbon atoms has also been carried out.
Chemical Physics Letters, 2011
This work builds on our recently published anisotropic potential for polycyclic aromatic hydrocarbons (PAH) [T.S. Totton, A.J. Misquitta, M. Kraft, J. Chem. Theory Comput. 6 (2010) 683] by developing a new transferable electrostatic model for PAH molecules. Using this model, the atomic charge parameters used in the PAH anisotropic potential may be rapidly calculated from a set of predefined parameters rather than from molecule-specific ab initio calculations. The importance of the out-of-the-plane quadrupolar moments is highlighted and they are used as the basis for an accurate and transferable electrostatic model for PAHs. This model exhibits an r.m.s. deviation of 1.7kJmol-1 - an order of magnitude less than previous models.►A new transferable intermolecular electrostatic model for PAH molecules. ► Based on physically significant quadrupole interactions. ► Resulting model is an order of magnitude more accurate the previous models. ► Rapid evaluation time is a significant benefit over ab initio models.
The Journal of Physical Chemistry A, 2008
We present an electrostatic interaction model for the calculation of the static electronic polarization of hydrocarbons. In previous work, models have often been presented for one single type of hydrocarbons. Here, we discuss the different requirements for a model to describe aliphatic, olephinic, and aromatic systems. The model is based on the representation of the carbon and hydrogen atoms by induced electric charges and dipoles, where the actual values of the charges and dipoles are those that minimize the electrochemical energy of the molecule. The electrostatic interactions are described in terms of normalized propagators, which improves both the consistency and the numerical stability of the technique. For the calibration of our model, we sought at reproducing the molecular polarizabilities obtained by current density functional theory for a set of 48 reference structures. We propose parameters for each type of hydrocarbon, which provide an excellent agreement with the reference data (relative error on the mean molecular polarizabilities of 0.5, 1.4, and 1.9% for alkanes, alkenes, and aromatic molecules, respectively). We also propose parameters based on the local environment of each atom, which are better suited for the description of more complex molecules. We finally study the polarizability of fullerenes and small hydrogen-terminated (5,5) carbon nanotubes.
Journal of Molecular Modeling, 2014
A systematic study of the electronic structure of polycyclic hydrocarbons from naphthalene to a system containing 80 fused benzene has been carried out. Geometries were optimized for closed shell singlet, open shell singlet, triplet and multiplet states at B3LYP/cc-pVDZ level of theory, D1 (second order Møller-Plesset) and D1 (second-order approximate coupled-cluster) diagnostics have been calculated for studied molecules. Complete active space self-consistent field (10,10)/6-31G(d) single point energy calculations have been carried out for all optimized structures. Multireference character of the ground state becomes important when the number of atoms in the polycyclic hydrocarbon exceeds 40-50. At this point, D1 diagnostics reaches 0.04-0.05 and the squared configuration interaction expansion coefficient for dominant configuration drops to about 0.6. However, only for the three largest systems predominantly polyradicalic ground states have been detected. All other polycyclic hydrocarbons showing significant multiconfigurational character of singlet ground state have only two dominant configurations which are closed shell singlet and doubly excited singlet, respectively. Thus, small polycyclic hydrocarbons have mostly single reference singlet ground state, the medium size systems have notably multireference ground state (singlet or triplet) with only moderate polyradicalic character. The ground state of largest systems is singlet polyradical.