Computational Physics

In this paper, we report a combined experimental and theoretical study on molecular structure; vibrational spectra of 2-hydroxy-3,5-dichlorobenzaldehyde (HDCB) have been recorded using Fourier transform infrared (FT-IR) and FT-Raman spectra in the region of 4000?400 cm^?1 and 3500?100 cm^?1, respectively. The conformational stability, molecular geometry and harmonic vibrational frequencies were obtained by HF/6-31++G(d,p) and B3LYP/6-31++G(d,p) basis set. The calculated harmonic vibrational frequencies were compared with experimental FTIR and FT-Raman fundamentals. The observed and calculated frequencies are found to be in good agreement. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The thermodynamic functions from spectroscopic data by statistical methods were obtained for the range of temperature 100 – 1000K.

Grand, a brand of groundnut oil was studied to investigate the effect of X-irradiation on its physicochemical properties. Different physicochemical parameters were characterized- the iodine value, free fatty acid (FFA) value, pH value and viscosity of the non-irradiated oil was obtained as 2.38, 1.83, 5.73 and 4.80 × 10-5m2/s respectively. The effect of X-irradiation on the oil showed a modification of the iodine value, Free Fatty Acid (FFA) value, pH value and viscosity to be 2.28, 2.86, 5.25 and 4.52 × 10-5m2/s when irradiated once. Also, 2.23, 3.25, 5.14 and 4.52 × 10-5m2/s when irradiated twice and 2.17, 3.70, 5.06 and 4.20 × 10-5m2/s when irradiated the third time. From the results of the investigated parameters, it was concluded that the oxidative deterioration level of the Grand oil can be used as a lubricant if the higher viscosity can be lowered and its oxidation stabilized appreciably.

A systematic vibrational spectroscopic assignment and analysis of sustiva(EFV) has been carried out by using FTIR, FT-Raman and UV spectral data. The vibrational analysis were aided by electronic structure calculations – ab initio (RHF) and hybrid density functional methods (B3LYP) performed with 6-31G(d,p) and 6-31++G(d,p) basis sets. Molecular equilibrium geometries, electronic energies, bond orders, natural bond order analysis, IR intensities, and harmonic vibrational frequencies have been computed. The assignments proposed based on the experimental IR and Raman spectra have been reviewed and selected assignment of the observed spectra have been proposed. UV–visible spectrum of the compound was also recorded and the electronic properties, such as HOMO and LUMO energies and ?max were determined by time-dependent DFT (TD-DFT) method. The thermodynamic functions of the title molecule were also performed using the RHF and DFT methods.

With the newly improved ansaltz for the wave function and adopting the modified approximation scheme to evaluate the centrifugal term, we solve the Schrödinger equation with Woods-Saxon plus Rosen-Morse Potentials analytically, for arbitrary l-state. We also obtain the bound state energy spectrum and the unnormalized real and imaginary wave function.

The unsteady gravity-driven convective flow and heat transfer of optically thick nanofluid past an oscillating, vertical plate is considered. The flow is confined to y > 0 where y is the coordinate measure in the normal direction to the plate. The fluid is assumed to be electrically conducting with an uniform magnetic field applied in a direction perpendicular to the plate. The resulting equation is solved by making use of Laplace transform method. Velocity profile and temperature profile are drawn for different values of radiation parameter and magnetic parameter.

In this work, experimental and theoretical study on the molecular structure, scaled quantum chemical calculations of energies and vibrational wavenumbers of 4-(dimethylamine) benzophenone (4DMBP) is presented. The vibrational frequencies of the title compound were obtained theoretically by DFT/B3LYP calculations employing the standard 6-311+G(d,p) and 6-311++G(d,p) basis sets for optimized geometry and were compared with Fourier transform infrared spectrum (FTIR) in the region of 4000 – 400 cm?1 and Fourier transform Raman spectrum in the region of 4000 – 100 cm?1. Complete vibrational assignments, analysis and correlation of the fundamental modes for the title compound were carried out. The vibrational harmonic frequencies were scaled using scale factor, yielding a good agreement between the experimentally recorded and the theoretically calculated values. The study is extended to calculate the HOMO-LUMO energy gap, NBO, mapped molecular electrostatic potential (MEP) surfaces, polarizability, Mulliken charges and thermodynamic properties of the title compound.

The purpose of this research was to compare the performance of different DFT methods at different basis sets in predicting geometry and vibrational spectrum of dopamine. The molecular structure and infrared spectrum of dopamine was studied. Quantum chemical calculations using density functional theory (DFT) with functions B3LYP, B3PW91, X3LYP, M06 and M06-2X at various basis set levels (6-311++G(d,p), 6-311++G(2d,2p) and Aug-cc-pVDZ) were performed. The computed result indicates that X3LYP/6-311++G(d,p) level is distinctly superior to all the remaining DFT methods in predicting molecular structure of dopamine. The vibrational spectral analysis indicates the B3LYP/6-311++G(2d,2p) level is better than the other methods at all the remaining basis sets.

The FT-IR and FT-Raman spectra of 2,4-dichloro-?,?,?-trifluorotoluene (D???TFT ) have been recorded in the range of 4000–400 cm-1 and 3500–50 cm-1 respectively. The molecular geometry and vibrational frequencies in the ground state are calculated using the LSDA and B3LYP method with 6-311+G(d, p) and 6-311++G (d, p) basis sets . The computed values of frequencies are scaled using a suitable scale factor to yield good coherence with the observed values. Most of the modes have wave numbers in the expected range. The calculated HOMO–LUMO energy gap shows that charge transfer occur within the molecule. NBO analysis has been performed in order to elucidate charge transfers or conjugative interaction, the intra-molecule hybridization and delocalization of electron density within the molecule. The total energy distribution (TED) has also been calculated for each mode of the vibration of the molecule.

In this work, FT-IR and FT-Raman spectra are recorded on the solid phase of methyl 2-chloronicotinate in the regions 4000–400 cm-1 and 3500–100 cm-1 respectively. The geometrical parameters, vibrational assignments, HOMO–LUMO energies and NBO calculations are obtained for the monomer and dimer of methyl 2-chloronicotinate from DFT (B3LYP) with 6-311++G (d, p) basis set calculations. Second order perturbation energies and electron density (ED) transfer from filled lone pairs of Lewis base to unfilled Lewis acid sites of methyl 2-chloronicotinate are discussed on the basis of NBO analysis. give the evidence for the formation of dimer entities in the title molecule. The theoretically calculated harmonic frequencies are scaled by common scale factor. The observed and the calculated frequencies are found to be in good agreement. The thermodynamic functions were obtained for the range of temperature 100–1000 K. The polarizability, first hyperpolarizability, anisotropy polarizability invariant has been computed using quantum chemical calculations. The chemical parameters were calculated from the HOMO and LUMO values. The NMR chemical shielding anisotropy (CSA) parameters were also computed for the title molecule.

The FT-Raman and FTIR spectra for 3-amino-4-methyl benzoic acid (AMBA) have been recorded in the region 4000–100 cm?1 and compared with the harmonic vibrational frequencies calculated by DFT method using B3PW91/6-31+G(d,p) and B3PW91/6-311++G(2d,2p) basis set with appropriate scale factors. IR intensities and Raman activities are also calculated by DFT methods. Optimized geometries of the molecule have been interpreted and compared with the reported experimental values for benzoic acid and some substituted benzoic acids. Furthermore, the molecular orbital calculations such as natural bond orbitals (NBO), HOMO-LUMO energy gap and Mapped molecular electrostatic potential (MEP) surfaces were also performed with the same level of DFT. The detailed interpretation of the vibrational spectra has been carried out with the aid of potential energy distribution (PED) results obtained from MOLVIB program.