Computational Physics

Theoretical studies were conducted on the molecular structure and vibrational spectra of 2-amino-5-bromo-4-methylpyridine (ABMP). The FT-IR and FT-Raman spectra of ABMP were recorded in the solid phase. The molecular geometry and vibrational frequencies of ABMP in the ground state have been calculated by using the ab initio HF (Hartree-Fock) /6-311+G(d,p) and density functional methods (B3LYP) invoking 6-311+G(d,p)/6-311++G(d,p) basis set. The optimized geometric bond lengths and bond angles obtained by HF method show best agreement with the experimental values. Comparison of the observed fundamental vibrational frequencies of ABMP with calculated results by HF and density functional methods indicates that B3LYP is superior to the scaled Hartree-Fock approach for molecular vibrational problems. 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 and FT- Raman, NMR spectra of ABMP was also reported. NBO analysis has been performed in order to elucidate charge transfers or conjugative interaction, the intra-molecule rehybridization and delocalization of electron density within the molecule. 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.

In this work, we report a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of Isobutyltrimethoxylsilane. Density functional theory (DFT),B3LYP/6-311++G (d,p) basis set was used for the optimization of the ground state geometry and simulation of the Infrared and Raman spectra of this molecule. Calculated geometrical parameters fit very well with the experimental ones.The Self Assembled Monolayer of Isobutyltrimethoxylsilane on Si/SiO2 substrate was prepared and the resulting surface was studied using AFM.

In this work, the experimental and theoretical vibrational spectra of N,N-dimethyl-m-anisidine (NNDMA, C9H13NO) (3-methoxy-N,N-dimethylaniline) were studied FT-IR and FT-Raman spectra of NNDMA in the liquid phase have been recorded in the region 4000–400 cm?1 and 3500–50 cm?1, respectively. The structural and spectroscopic data of the molecule in the ground state have been calculated by using density functional method (B3LYP) with the 6-31G and 6-311++G(d) basis sets. The complete assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The calculated HOMO and LUMO energies show that charge transfer occur in the molecule. Besides, molecular electrostatic potential (MEP) and thermodynamic properties were performed. The other molecular properties like Mulliken population analysis and polarizabilities of NNDMA were reported.

The FT?IR and FT?Raman spectra of benzyl fluoride were recorded and analyzed. The vibrational wavenumbers were examined theoretically with the aid of the GAUSSIAN 09 package of programs using the HF/6?311++G(d,p) and B3LYP/6?311++G(d,p) levels of theory. The data obtained from vibrational wavenumber calculations are used to assign vibrational bands obtained in IR and Raman spectroscopy of the studied molecule. The first hyperpolarizabililty, NBO, HOMO-LUMO, infrared intensities and Raman intensities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive object for future studies of non?linear optics. The geometrical parameters of the title compound are in good agreement with the values of similar structures.

We have studied the formation of quantum ion acoustic shock waves (QIASWs) in a three component unmagnetized plasma, whose constituents are electrons, ions and immobile positrons.  The effects of both the dissipation due to the plasma kinematic viscosities and the dispersion caused by the Bohm potential are taken into account.  Employing reductive perturbation method, we have obtained the deformed Korteweg-deVries Burger (dKVB) equation for quantum ion acoustic shock wave in planar geometry.  From our numerical analysis, we have studied the effect of the quantum parameter H and ion kinematic viscosities (h­_i0) of the planar dKdVB on different values of the positron concentration P.

In this work, the vibrational characteristics of 1-hydroxynaphthalene-2-carboxylicacid (1HN2CA) have been investigated and both the experimental and theoretical vibrational data indicate the presence of functional groups in the title molecule. The density functional theoretical (DFT) computations were performed at the B3LYP/(ccPVDZ, 6-311+G(d)) levels to derive the optimized geometry, vibrational wavenumbers with IR and Raman intensities. Furthermore, the molecular orbital calculations such as natural bond orbital’s (NBOs), HOMO–LUMO energy gap 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.

The Fourier transform Raman (FT-Raman) and Fourier transform infrared (FTIR) spectra for Lamivudine in the solid phase have been recorded in the region 4000–100 and 4000–400 cm ^-1 , respectively, compared with the harmonic vibrational frequencies calculated using density functional theory (DFT) (B3LYP) and Restricted Hartee Fock (RHF) method by employing 6-31G (d,p) basis set with appropriate scale factors. Optimised geometries of the molecule have been interpreted and compared with the reported experimental values. The experimental geometrical parameters show satisfactory agreement with the theoretical prediction from DFT. The scaled vibrational frequencies seem to coincide with the experimentally observed values with acceptable deviations. The theoretical spectrograms (IR and Raman) have been constructed and compared with the experimental FTIR and FT-Raman spectra. The UV spectrum was measured in methanol. In order to gain some insight into the recorded spectrum, the quantum mechanical calculations were performed for Lamivudine using TD DFT with B3LYP/6-31G(d,p) basis set. The optimized molecular geometry, bond orders, harmonic vibrational wavenumbers of Lamivudine were calculated by Restricted Hartree Fock and Density functional B3LYP method with the 6-31G(d,p) basis set using Gaussian 03W program.

Alagankulam region covering Tamilnadu in Southern India has numerous cultural heritages due to its witness to various social movements of different civilizations in ancient times. Archaeological excavations carried out at different depths of the trench revealed the most significant findings of pot shred, roulette ware and amphorae jar pieces and pieces of red ware etc. These relics are dated back to 3rd - 4th century. In this study, pot shred of grey ware unearthed from Alagankulam site were investigated by FT-IR spectrometry. Energy dispersive X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses were used as complementary techniques in order to expose chemical and mineralogical phase contents respectively. Obtained results showed that these potteries have been produced with non-calcareous clays and include moderate amounts of MgO, K2O, Na2O and Fe2O3 in this context. Additionally, high temperature phases have also been detected with XRD analyses in some samples.

Abacavir (ABC) {(1S,4R)-4-[2-amino-6-(cyclopropylamino)-9H-purin-9-yl] cyclopent-2-en-1-yl} methanol, is an antiretroviral medication which is used to prevent and treat HIV/AIDS. It belongs from nucleoside analog reverse transcriptase inhibitor (NRTI) a sub class of RTIs, which interrupt the virus to make copy of it. In this paper we reported the results of a systematic experimental IR and Raman study of Avacavir. Additionally the equilibrium geometry, harmonic vibrational frequency Raman and IR intensities were calculated using density function theory. Finally complete vibrational assignment of Abacavir is given for the observed Raman and Infrared spectra. The experimental and theoretical results are found to be in excellent agreement with each other. We believe that the results obtained herein will prove to be an excellent starting point for studying the detailed potential surface of the molecule which is needed to understand the drug receptor interactions.

Vibrational spectral analysis was carried out for  Methyl m-hydroxy benzoate (MMHB) and Methyl salicylate (MS) by using the FTIR and FT-Raman spectroscopy in the range of 4000cm^-1-400cm^-1 and 4000cm^-1-50cm^-1 respectively. The theoretical computational density functional theory (DFT/B3LYP) was performed at 6-31G** levels to derive equilibrium geometry, vibrational wavenumbers, infrared intensities and Raman scattering activities. The complete vibrational assignment was performed on the basis of the potential energy distribution (PED), calculated with scaled quantum mechanics (SQM) method. Quantum chemical parameters such as the highest occupied molecular orbital energy (E_HOMO), the lowest unoccupied molecular orbital energy (E_LUMO), energy gap (?E), chemical potential (P_i), global hardness (?),and the softness (?), were calculated. The theoretical electronic absorption spectra have been calculated by using CIS methods. ¹H and ¹³C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by using gauge invariant atomic orbital (GIAO) method. The total atomic charges, natural charges and thermodynamic parameters were also calculated. As expected, the results show the greater stability and stronger hydrogen bond between oxygen and ester group.