We present the procedure for transforming delocalized molecular orbitals into the localized property‐optimized orbitals (LPOs) designed for building the most accurate, in the Frobenius norm sense, ...approximation to the first‐order reduced density matrix in form of the sum of localized monoatomic and diatomic terms. In this way, a decomposition of molecular properties into contributions associated with individual atoms and the pairs of atoms is obtained with the a priori known upper bound for the decomposition accuracy. Additional algorithm is proposed for obtaining the set of “the Chemist's LPOs” (CLPOs) containing a single localized orbital, with nearly double occupancy, per a pair of electrons. CLPOs form an idealized Lewis structure optimized for the closest possible reproduction of one‐electron properties derived from the original many‐electron wavefunction. The computational algorithms for constructing LPOs and CLPOs from a general wavefunction are presented and their implementation within the open‐source freeware program JANPA (http://janpa.sourceforge.net/) is discussed. The performance of the proposed procedures is assessed using the test set of density matrices of 33 432 small molecules obtained at both Hartree‐Fock and second‐order Moller‐Plesset theory levels and excellent agreement with the chemist's Lewis‐structure picture is found.
Algorithms for transforming molecular orbitals to localized form are presented. The orbitals created by the proposed algorithms provide the basis for accuracy‐optimized decomposition of any one‐electron molecular property into contributions associated with individual atoms and the pairs of atoms. In this way, the “property‐optimal” Lewis structure is recovered from a general wavefunction obtained from quantum‐chemical calculations. The algorithms are implemented in an open‐source freeware program JANPA (http://janpa.sourceforge.net/) and tested on 33 432 small molecules.
•Computational studies for the formation of Hydrogen Cyanide (HCN) molecule in interstellar medium.•Effect of temperature on Enthalpy, Entropy and Gibbs free energy of HCN molecule.•Formation of HCN ...through hydrogenation of CN radical.•Proposed Reaction paths are highly feasible in interstellar medium.•Feasibility of reaction mechanism has been also confirmed by calculating Rate coefficient.•This work has been studied with HF and DFT (at different functionals, viz. B3LYP, B3PW91 & WB97XD) methods using 6-31G++(d,p) basis set by Gaussian 09 software.
In the recent studies it is observed that not only ion/radical-molecule gas-phase reactions, but also solid-state reactions on icy dust grains play an important role for the formation of new species. Molecular hydrogen (H2) is the most abundant molecule in the interstellar medium (ISM) in gas phase and it has been assumed to exist in solid state or as coating on grains. The work is mainly focused on the hydrogenation of CN radical in interstellar ice analogs for astronomically relevant temperatures. The solid H2 can act as a hydrogenation agent, reacting with CN radicals to form HCN. Hydrogenation reactions of CN radical have been studied by Hartree-Fock (HF) and Density Functional Theory (DFT) methods. We have discussed that, how molecules form when CN containing ices are exposed to thermal hydrogen atoms. The present work deals with possibility of the formation of HCN by hydrogenation via radical molecule reactions in gas phase as well as in PCM and the effect of temperature on thermodynamical parameter.
Investigations of intermolecular interactions are of great interest and many studies in this field focus on the use of theoretical computational chemistry. Commonly the systems of interest comprise ...molecules with hundreds of atoms, limiting the use of ab initio theoretical methods. In order to investigate the accuracy of different quantum chemical methods, a systematic study was carried out involving 15 inclusion complexes of α-cyclodextrin and 28 complexes of β-cyclodextrin. The accuracy of semiempirical methods in geometry prediction was evaluated in comparison to crystallographic data, with AM1 and PM3 showing the best results. Subsequently, the accuracy of semiempirical methods in predicting both geometry and interaction energy was studied using the results of DFT calculation as reference, with and without dispersion correction. The best method was B3LYP/6-31G(d,p) with D3 correction, followed by PM6 with D3 correction with similar accuracy. However, as the DFT method require a high computational cost for large systems, PM6-D3 is the method recommended for the systems studied here. The main conclusion is the need to develop a semiempirical method capable of correctly describing the interaction energy, which must correspond to an accurate geometry.
•Study of the correction dispersion in quantum chemical methods for cyclodextrin-guest.•The best geometries descriptions were obtained with AM1 and PM3 for cyclodextrins.•The uncorrected DFT energies were inaccurate even when the geometry is accurate.•The inclusion of D3 correction is crucial to obtain accurate energies .
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•Proton sponges are used in various research applications.•The used basis set was def2tzvp, which is popular, flexible, and accurate.•Graphical data and error analysis suggest the ...dominance of M062X functional.•Dispersion corrections are not significant in finding the basicity of small molecules.•The M062x function has a slight advantage in predicting structural properties.
Proton affinities and gas phase basicities, starting from small molecules like ammonia up to proton sponge like PMG (N,N,N|,N|,N|-Pentamethylguanidine) were calculated with cost-effective, but accurate computational methods B3LYP, BP86, PBEPBE, APFD, wB97XD, and M062X using the flexible def2tzvp basis set and compared with experimental results. Different error methods were used to study the variations from experimental results. Most of these methods gave good results, but M062X was slightly better with minimum error in all examples containing hetero atoms. The APFD and wB97XD functionals tend to overestimate values and do not perform as well. The effectiveness of Grimme's dispersion corrections on the basicity was also tested, but found to be ineffective. The accuracy of different functionals in predicting the NN bond length in DAN (1,8-Diaminonaphthalene) and DMAN(1,8-bis(dimethylamino) naphthalene was tested. APFD, wB97XD and M062X agree well with reported values.
Nanotechnology that develops novel materials at size of 100nm or less has become one of the most promising areas of human endeavor. Because of their intrinsic properties, nanoparticles are commonly ...employed in electronics, photovoltaic, catalysis, environmental and space engineering, cosmetic industry and – finally – in medicine and pharmacy. In that sense, nanotechnology creates great opportunities for the progress of modern medicine. However, recent studies have shown evident toxicity of some nanoparticles to living organisms (toxicity), and their potentially negative impact on environmental ecosystems (ecotoxicity). Lack of available data and low adequacy of experimental protocols prevent comprehensive risk assessment. The purpose of this review is to present the current state of knowledge related to the risks of the engineered nanoparticles and to assess the potential of efficient expansion and development of new approaches, which are offered by application of theoretical and computational methods, applicable for evaluation of nanomaterials.
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Diazene is the smallest member of the azo compound which has distinct chemical properties widely used in synthetic chemistry. In order to understand the structures and properties of diazene through ...different stages, the intermolecular interactions need to be studied. We have reported the many-body interactions of linear and cyclic diazene oligomers (mono to pentamer) in gas and water solvent in addition to spectroscopic characterization. It is observed that the sum of two body interaction energy contributes more to binding energy than relaxation energy. Upon solvation, significant changes have been observed in infrared and electronic absorption spectra of linear and cyclic diazene oligomers in the gas phase compared to the water solvent state.
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•Spectroscopic study of linear and cyclic diazene oligomers in gas and water solvent.•Upon solvation, significant changes observed in the spectroscopic characterization.•NTOs studied for diazene oligomers in gas & solvent, IEFPCM used for solvent effect.•Many-body interaction of linear and cyclic diazene oligomers in gas and water solvent.•Sum of 2-body interaction contributes more to binding energy than relaxation energy.
The present study reports the many-body analysis and spectroscopic characterization of linear and cyclic diazene oligomers in gas and water solvent states. The oligomers of diazene from monomer to pentamer have been considered for the study. The spectroscopic studies such as geometrical parameters, infrared spectra, electronic absorption spectra, and natural transition orbitals (NTOs) were reported. Many-body analysis techniques have been implemented to study the interactions among the diazene oligomers. These calculations have been performed using exchange and correlation functional (B3LYP) and 6-311++G (d,p) basis set. The geometrical parameters and infrared modes of monomer diazene in the gas state are well-matched with the available experimental determinations at this level of theory. A significant change in vibrational modes of linear and cyclic diazene oligomers has been observed in the phase-to-water solvent state. The time-dependent density functional theory (TD-DFT) has been used to calculate the electronic absorption spectra of diazene oligomers. The Wavelength of electronic transitions, oscillator strength, and HOMO to LUMO gap has been reported. Many-body analysis shows that two-, three-, four-, and five-body energies have a remarkable contribution to the binding energy in addition to relaxation energies. All these calculations have been performed using Gaussian 16 program package.
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The transition metal complexes are playing the crucial role in advancement of modern chemical science. In the present study, we synthesized the Pd(II) complex Pd2 ...(C5H5F3N2)2(C5H4F3N2)2Cl2·3(C2H6O), 1 with 3-Methyl-5-(trifluoromethyl) pyrazoleligand. The complex 1 has been characterized by IR spectroscopy, elemental analysis and X-ray crystallography. The complex 1 crystallizes in triclinic space group P-1. Moreover, density functional theory (DFT) methods are successfully used not only to study the optical and nonlinear optical (NLO) properties of complex 1 but also to design its potential derivatives with Ni(II) and Pt(II) metals as complexes 2 and 3, respectively. The interaction energies are calculated for optimized complexes that are found to be −400, −524.41 and −504.16 kcal/mol for complexes 1, 2 and 3, respectively. The calculations for third-order nonlinear optical polarizability (γ) show that the average γ amplitudes for compounds 1, 2 and 3 are found to be 79.89 × 10−36, 71.24 × 10−36 and 102.09 × 10−36 esu, respectively. The γ amplitudes of compounds 1, 2 and 3 are about 4 times, 3 times and 5 times larger than that of para-nitroaniline (pNA), which is a prototype NLO molecule, respectively. The calculations of UV–Visible spectra show that the maximum absorption wavelength for complex 3 is around 260 nm with a significantly larger oscillator strength, which is about 4 times larger than the absorption spectra of complexes 1 and 2. The analysis of FMOs shows the ligand to metal intramolecular charge transfer (LMCT) process which might be the reason of larger NLO response properties in complex 3. Additionally, the calculations of global chemical reactivity descriptors indicate that the complexes are thermally and kinetically stable. Thus, we believe the present study will intrigue the scientific community to explore the designed complexes for optical and NLO applications.
Organocatalyzed Michael addition of N‐substituted tetramic acids to nitroalkene acceptors followed by O‐alkylation gave polyfunctionalized tetramic acid (31 examples, 59–94% ee). The ...enantioselectivity of the product was influenced by the N‐substituent of the substrate. Quantum chemical methods provided the mechanistic insights of the studied transformation. The preferred reaction pathway follows the model proposed by Pápai et al. Single crystal structure confirmed the absolute configuration, which was in line with the ECD measured and calculated structure. Additionally, a comparative study of the alkylation of a selected tetramic and tetronic acid with trans‐β‐nitrostyrene is disclosed. Follow‐up amidations demonstrated the applicability of this class of compounds for the incorporation into both dipeptide and depsipeptide sequences.
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