Computational Chemistry

Extensive quantum chemical calculations of energy, geometrical structure, harmonic vibrational frequencies and the construction of theoretical spectrograms of IR and Raman spectra of the molecule, methyl 2,4-dihydroxy-6-methyl benzoate(methyl orsellinate) have been carried out by Hartree-Fock (HF) and Density Functional Theory (DFT/B3LYP) method with 6311++G(d, p) basis set. The assignments of normal modes of the vibration of the title molecule along with the observed frequencies (FT-IR and FT-R) and scaled frequencies have been obtained by HF/DFT computation. The simulated NMR spectra are obtained by (GIAO) gauge independent atomic orbital method and their chemical shifts are compared with the experimental 13C NMR and 1H NMR spectra. Molecular geometric parameters, dipole moment, mullikan charge, thermodynamic properties, FMO analysis and NLO properties have also been computed and discussed in a detailed manner.The electrostatic potential surface and the mullikan charge analysis indicates that the oxygen atoms of the molecule act as reactive centers for nucleophilic attack .The temperature dependence of the thermodynamic properties such as entropy (S), enthalpy (H) and heat capacity (Cp) from 50K to 700K were also determined.

The electronic absorption spectra of 3,5-diamino-1,2,4-triazole was recorded in the region of 190-450 nm. Quantum chemical calculations of energies, geometrical structures and electronic absorption spectra of 3,5-diamino-1,2,4-triazole were carried out by ab initio HF/6-31+G*, DFT (B3LYP/6-31+G*) and TD-DFT /B3LYP/6-31+G* level of theory with complete relaxation in the potential energy surface. The Mulliken charge analysis indicates that the nitrogen atoms of the triazole ring and the amino group attached to the ring are the main reactive centers of 3,5-diamino-1,2,4-triazole. The calculated HOMO-LUMO energies show that the molecule has low energy gap which implies low kinetic stability and high chemical reactivity. The study is extended to the analysis of dipole moment, EHOMO, ELUMO both in the gas phase and in the presence of solvent for comparison. Thermodynamic properties were also calculated and discussed. The calculated values of absorption wavelengths are compared with the experimental data for this molecule as a means of validation of the theoretical model used. The predicted results are in excellent agreement with the experimental ones.

(E)-N1-(2-(4-isobutylphenyl)propylidene)benzene-1,2-diamine, an organic material has been synthesized and their chemical structure was confirmed by means of elemental analysis, FT-IR, 1H and 13C NMR spectral techniques. The molecular geometry has been interpreted with the aid of structure optimization based on DFT/B3LYP and HF methods with 6-31G(d,p)level theory. The SXRD data were compared with the optimized parameter. Optimized geometry parameters are very well agrees with the reported one. FT-IR spectrum is recorded at room temperature. Functional group assignment was discussed on the B3LYP and HF level theories. The chemical reactivity and charge density of the compounds was obtained by Mulliken and MEP surfaces. The energy gap, electronic properties were measured and discussed. The intramolecular charge transfer interaction and ?-electron cloud movement in title molecule must be responsible for the NLO properties.

The electrical characteristics and molecular orbital analysis of 1,2-di(cyclopenta-1,3-dienyl)ethyne molecule has been studied by using quantum chemical calculations coupled with density functional theory (DFT) using Gaussian09 program package. The molecule has been substituted with thiol, Au and Pt atoms at both ends of the molecule one by one and the corresponding variations in structural, electrostatic and transport properties have been analyzed. In this study, thiol atom acts as linker whereas Au and Pt atoms act as electrodes. Comparing with thiol substituted molecule the Au and Pt substituted molecules exhibit more variations in their structural properties. Atomic charges of the free molecule as well as all the substituted molecules have been compared with MPA and NPA charges. The HOMO-LUMO gap (HLG) of the molecule decreases gradually for S, Au and Pt substituted molecules respectively. The existence of small HLG of Au substituted molecule enhances the conductivity. Using Au as electrodes with thiol as linker, 1,2-di(cyclopenta-1,3-dienyl)ethyne can acts as an efficient molecular wire.

The geometries, electronic structures, polarizabilities, and hyperpolarizabilities of organic dye sensitizer 1,4-Phenylenediacetonitrile was studied based on ab initio HF and Density Functional Theory (DFT) using the hybrid functional B3LYP. Ultraviolet-visible (UV-Vis) spectrum was investigated by Time Dependent DFT (TDDFT). Features of the electronic absorption spectrum in the visible and near-UV regions were assigned based on TDDFT calculations. The absorption bands are assigned to ???* transitions. Calculated results suggest that the three excited states with the lowest excited energies in 1,4-Phenylenediacetonitrile is due to photo induced electron transfer processes. The interfacial electron transfer between semiconductor TiO2 electrode and dye sensitizer 1,4-Phenylenediacetonitrile, is due to an electron injection process from excited dye to the semiconductor’s conduction band. The role of cyanine and methyl group in 1,4-Phenylenediacetonitrile in geometries, electronic structures, and spectral properties were analyzed.

The vibrational spectroscopy of 1-isopropyl-4-methyl benzene [IMB] by means of quantum chemical calculation has been studied. The FT-Raman and FT-IR spectra of IMB have been recorded in the region 3500-50cm-1 and 4000-400cm-1 respectively. The fundamental vibrational frequencies and intensity of vibrational bands have been evaluated using HF and density functional theory (DFT) with standard B3LYP/6-31+G(d,p) and HF/6-31+G(d,p) basis set combinations for optimized geometries. The observed FT-IR and FT-Raman vibrational frequencies have been anlaysed and compared with theoretically predicted vibrational frequencies. The assignments of bands to various normal modes of molecule have also been carried out. The electric dipole moment (?) and the first hyper polarazibility (?) values of the investigated molecule have been computed using DFT calculations. The calculated HOMO and LUMO energies show that charge transfer occur with in the molecule.

Most of the interstellar protonated molecules that have been shown to be astronomically detectable based on recent studies could be termed as 'non-terrestrial' species as a number of them are yet to be probed in the terrestrial laboratory, thus, the rotational transitions required for their astronomical searches are not available. In this study, the coupled cluster variant CCSD(T) together with the aug-cc-pVTZ basis set has been used to predict the spectroscopic parameters of four known neutral interstellar molecules and their corresponding protonated analogues of which two; H2NCO+ and H2COH+ have been astronomically detected. The protonated analogues of H2NCN and H2CS are potential interstellar species from recent studies. The predicted rotational constants/transitions are in good agreement for those with known experimental data, thus, these spectroscopic parameters could guide the astronomical searches and laboratory measurement of these species without experimentally determined spectroscopic constants.

Engineering industry, mostly steel are heats treated under controlled sequence of heating and cooling to alter their physical and mechanical properties to meet desired engineering applications. In this study, the effect of heat treatment (Isothermal annealing process, full annealing and normalizing) on the microstructure, fracture section and some selected mechanical properties of ingot 30CrMoV9 steel such as ultimate tensile strength, tensile yield strength, percentage reduction, percentage elongation, toughness and hardness. Sample of steel was purchased from local market and the spectrometry analysis was carried out. The steel samples were heat treated in an electric furnace at different temperature levels, holding times and then cooled in different media. The mechanical properties of the treated and untreated ingot samples were determined using standard methods. Results showed that the mechanical properties of ingot 30CrMoV9 steel can be changed and improved by various heat treatments for a particular application. It was also found that the full annealed samples with mainly ferrite structure gave the lowest tensile strength and hardness value and highest ductility and toughness value. While normalizing sample which comprise martensite gave the highest tensile strength and hardness value and lowest ductility and toughness value.

Quantum chemical calculations offer the real promise of being able to complement experiment as a means to uncover and explore new areas in chemistry. One of such is its use in the determination of molecular structure, kinetics and reactivity. This work seeks to investigate the molecular properties of Oxygen monofluoride (OF) and its two possible protonated analogues (HOF+ and HFO+). Quantum chemical methods; Hartree fock (HF), Becke-3-Lee-Yang-Parr (B3LYP), Moller-Plesset second order (MP2), Coupled Cluster method (CCSD) and Gaussian 04 method (G4) with varying basis sets were employed in the determination of the parameters (Dipole moment, bond distance, IR frequency, zero point vibrational energy, and rotational constants) reported for the three molecular species studied in this work. Bond angle was reported for the two protonated analogues (HOF+ and HFO+). From the results as compared to the experimental values, B3LYP/6-311++G** method proves itself as the best method in the optimization and frequencies calculations of the OF, HOF+ and HFO+ because it gives better accuracy in most of the calculated parameters and the MP2 method also give relative accuracy in some of the calculated parameters of OF and its protonated analogues, HOF+ and HFO+. The optimized geometry shows the OF molecule to be linear while the protonated analogues were non-linear.

This work deals with the vibrational spectroscopy of 2’, 4’-difluoro acetophenone (DFA) and 4’-chloro acetophenone (CA). The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) using standard B3LYP/6-31G** method and basis set combinations. The vibrational spectra were interpreted, with the aid of normal coordinate analysis based on a scaled quantum mechanical force field. The infrared and Raman spectra were also predicted from the calculated intensities. The effects of halogen substituents on the structure and vibrational frequencies have been investigated. Comparison of simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.  The ¹³C and ¹H NMR chemical shifts of the DFA and CA molecules were calculated using the Gauge-Invariant- atomic orbital (GIAO) method in DMSO solution using IEF-PCM model and compared with experimental data.