Computational Physics

The optimized molecular geometry, normal mode wavenumbers, infrared intensities, corresponding vibrational assignments and atomic charges were investigated with the help of DFT/B3LYP method using 6-311++ G(d,p) basis set. The FT-IR spectrum of 2, 6-diphenyl-4H-pyran-4-one (DPO) has been recorded in the region 4000-400 cm-1. For the comparison between calculated and experimental results, assignments of fundamental modes were examined. The stability and charge delocalization of the molecule were studied by natural bond orbital (NBO) analysis. In addition, a molecular electrostatic potential map (MEP) of the title compound was studied to predict the reactive sites. The reactivity of the compound of interest was described by HOMO - LUMO energies and global descriptors. The electronic properties were also studied and the transition corresponds to ???*. The title compound exhibited good nonlinear optical activity and ten times greater than that of urea.

Normal coordinate calculations of 3-nitropyrrole have been carried out using Wilson’s FG matrix Valence Force Field (GVFF) for both in-plane and out-of-plane vibrations. The potential energy constants obtained in this study are refined using numerical methods. Keywords: FT-IR, FT-Raman, 3-nitropyrrole, Normal coordinate analysis, potential energy distribution.

The molecular vibrations of 2-bromo-4,6-dinitroaniline (BDNA) were investigated in solid phase, at room temperature by FT-IR and FT-Raman spectroscopy. The molecular geometry and vibrational frequencies of BDNA in the ground state were calculated by using the Hartree-Fock (HF) and density functional theory (DFT) methods (B3LYP) with 6-311++G** as basis set. Comparison of the observed fundamental vibrational frequencies of BDNA with calculated results by HF and density functional methods indicates that B3LYP is superior to HF method for molecular vibrational problems. The Mulliken atomic charges have also been computed at HF/6-311++G** and B3LYP/6-311++G** level. Finally the calculated HOMO and LUMO energies show that charge transfer occur in the molecule.

The understanding of optimized molecular geometry, vibrational analysis of the heterocyclic organic compounds plays a vital role in the process of drug discovery. The present work provides geometrical parameters, vibrational assignments for pharmaceutical intermediate 3-hydroxynaphthalene-2-carboxylicacid (3HN2CA). Moreover, the present study aims to illustrate how intermolecular interactions appear within the molecule on account of HOMO-LUMO studies. In addition to these, Mullikan’s Atomic charges associated with each atom are also reported. Entire vibrational, geometrical parameters, Mullikan’s Atomic charges and HOMO-LUMO Energy gap of 3HN2CA were predicted with the aid of B3LYP level of theory with cc/PVDZ and 6-31+G(d) basis sets on a quantum chemical software Gaussian 09W. In view of visual inspection, 60 normal modes of vibrations contributed to 3HN2CA were found out. Furthermore, the molecular orbital calculations such as natural bond orbital’s (NBOs) and Mapped molecular electrostatic potential (MEP) surfaces were also performed with the same level of DFT. The thermal flexibility of molecule in associated with vibrational temperature was also illustrated on the basis of correlation graphs. The detailed interpretation of the vibrational spectra has been carried out with the aid of potential energy distribution (PED) results obtained quantum chemical calculations. The delocalization of electron density of various constituents of the molecule has been discussed with the aid of NBO analysis.

Diphenyl ketone (DPK), a semi-organic nonlinear optical material, has been synthesized and single crystals were grown from alcohol – ethanol solution at room temperature up to dimensions of 4.5cm×4.5cm×4cm. The unit cell parameters were determined from single crystal and powder X-ray diffraction studies. The structural perfection of the grown crystal has been analyzed by X-ray diffraction (XRD) study. The variation of dielectric properties of the grown crystal with respect to frequency has been investigated at different temperatures. Microhardness measurements revealed the mechanical strength of grown crystal. The relative second harmonic efficiency of the compound is found to be 1.4 times greater than that of KDP. And the theoretical studies were conducted on the molecular structure and vibrational spectra of diphenyl ketone (DPK). The FT-IR and FT-Raman spectra of DPK were recorded in the solid phase. The molecular geometry and vibrational frequencies of DPK in the ground state have been calculated by using the density functional methods (B3LYP) invoking 6-311++G(d,p) and 6-311+G(d,p) basis set. The optimized geometric bond lengths and bond angles obtained by DFT method show best agreement with the experimental values. A detailed interpretation of the FT-IR and FT- Raman, Mullikan spectra of DPK was also reported. NBOs are localized electron pair orbitals for bonding pairs and lone pairs. UV–VIS spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies, were performed by time dependent density functional theory (TD-DFT) approach. Finally the calculations results were applied to simulated infrared and Raman spectra of the title compound which show good agreement with observed spectra. And the temperature dependence of the thermodynamic properties of constant pressure (Cp), entropy (S) and enthalpy change (?H0?T) for DPK were also determined. Keywords: DPK, HOMO- LUMO, UV, NBO, Mullikan, MEP.

The molecular vibrations of 2-methylnaphthalene was investigated by FT-IR and FT-Raman spectroscopies. Normal coordinate calculations of 2-methylnaphthalene have been carried out using Wilson’s FG matrix mechanism on the basis of General Valence Force field (GVFF) for both in-plane and out-of-plane vibrations. The potential energy constants obtained in this study are refined using numerical methods.

In the present work, the vibrational spectra of 1,2,4-trichloro-5-nitrobenzene (TCNB) was studied to identify the various normal modes with greater wave number accuracy. Density functional theory (DFT) calculations have been performed to support the wave number assignments. Further, density functional theory (DFT) combined with quantum chemical calculations was implemented to determine the first-order hyperpolarizability. The calculated HOMO and LUMO energies shows that charge transfer occur within the molecule. Electronic excitation energies, oscillator strength and nature of the respective excited states were calculated by the closed-shell singlet calculation method.

The experimental and theoretical study on the structure and vibrations 1h-1,2,4-triazole-3-thiol and 2-amino-1,3,4-thiadiazole have been carried out by DFT/B3LYPand DFT/LSDA method with 6-311++G(d,p) basis set. Utilizing the observed FT-IR and FT-Raman data, a complete vibrationalassignment and analysis of the fundamental modes of the title compounds were carried out. The vibrational frequencies which determined experimentally and compared with thosetheoretical frequencies from force field calculation based on B3LYP/6-311++G(d,p) method. Stability of the compound arising from hyper conjugative interactions and charged localization has been analyzed using natural bond orbital analysis. The 1H and 13C nuclear magneticresonance (NMR) chemical shifts of the compounds were calculated by the gauge independentatomic orbital (GIAO) method and compared with experimental results.

The Fourier-transform infrared spectrum of 3, 5-dimethylpiperidine (DMP) was recorded in the region 4000-400cm-1. The Fourier-transform Raman spectrum of DMP was also recorded in the region 3500-50 cm-1. Quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of DMP were carried out ab initio HF and density functional theory (DFT/B3LYP) method with 6-31+G (d,p) basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The values of the total dipole moment (µ) and the first-order hyperpolarizability(?) of the investigated compound were computed using ab initio quantum mechanical calculations. The calculated results also show that the DMP might have microscopic nonlinear optical (NLO) behavior with non-zero values. The difference between the observed and scaled wave number values of most of the fundamentals is very small. A detailed interpretation of the FT-IR, FT-Raman, NMR spectra of DMP was also reported. Natural bond orbital analysis has been carried out to explain the charge transfer or delocalization of charge due to the intra-molecular interactions. Energy of the highest occupied molecular (HOMO) orbital and lowest unoccupied (LUMO) molecular orbital have been predicted. Temperature dependence of various thermodynamic properties like heat capacity, enthalpy, Gibb’s free energy, entropy is increase with increase in temperature.

This paper analysed the possibility of expansion of Nekede Mechanic-Village gully located in Imo State Nigeria using Geotechnical tests method. The gully site is located on longitude 7o 2’ 6”E and latitude 5o 27’ 46”N. The analysis of the Geotechnical tests showed that Site Areas 3 and 4 are structurally week and susceptible to erosion due to their poor Shear Strength and Bulk Density values – in addition to being Non-Plastic. In contrast, site areas 1 and 2 are relatively stable. Sites 3 and 4 are located close to residential areas thus demanding desperate attention from government agencies before the expanding gully wreaks havoc.