Computational Physics

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.

The 2',4'-difluoroacetophenone (DFAP) molecule has been characterized by Nuclear magnetic resonance (NMR) spectroscopy. Density functional theory (DFT) calculation using B3LYP have been performed to investigate the molecular structure and 1H and 13C chemical shifts of the title molecule. The obtained results show that the calculated NMR chemical shifts are in a good agreement with experimental data.

This study has been carried out of calculating potential energy curves (Deng-Fan potential and Varshni potential) of ground state of diatomic molecule (HCl). Potential energy curves depended on spectroscopic Parameters (?e, ?exe, re, ?, µ, ?, De ,) and our results have been compared with experimental results.

In this work, the Fourier transform Raman and Fourier transform infrared spectra of 2-Methylidene -4-oxo-4-[(2, 4, 5-trichlorophenyl) amino] butanoic acid were recorded. The structural and spectroscopic analyses of the above compound were made by using B3LYP/ DGDZVP2 and DGTZVP basis sets. The detailed interpretation of the vibrational spectra has been carried out with the aid of VEDA program. The observed and calculated frequencies are found to be in good agreement. NMR spectra have been recorded and analysed. To investigate microscopic second order non linear optical behavior of the title compound, the electric dipole moment ?, the polarizability ? and hyper polarizability ? were computed. According to our calculation, the title compound exhibiting non-zero ? total value revealing microscopic second order NLO behavior. The value of HOMO-LUMO, Mulliken and natural charges have been calculated and analyzed. The natural bond orbital analysis confirms the occurrences of intra-molecular charge transfer interaction. Electrostatic potential surface has been plotted for predicting the structural activity relationship. Global reactivity descriptors and Fukui functions have been calculated for predicting the chemical reactivity and the stability of the chemical system. To test the biological activity of the title compound docking studies have been carried out.

In this work Laser Raman spectroscopy was used for spectroscopic characterization of chronic lymphocytic leukemia (CLL) blood samples. Eight samples collected from leukemia patient's type (CLL) were investigated using laser Raman spectrometer. The patients were diagnosed by histopathologies in Radiation and Isotopes Center Khartoum (RICK) and Alamal Hospital. The analysis of the Raman spectra was done for the peaks of proteins, lipids and nucleic acid. Significant differences in the spectra of CLL samples, compared with normal blood spectrum, were noticed. The results showed that Laser Raman spectroscopy can be used to diagnose efficiently the CLL via the spectral changes in the intensities of the spectral peaks and the changes in their Raman shifts.

Epivir is an anti HIV agent belonging to the class of nucleosides reverse transcriptase inhibitors. These drugs interrupt the virus to make copy of it. A systematic quantum chemical study and vibrational spectra of Epivir has been reported. Structure and spectral characteristic of Epivir have been studied using vibrational spectroscopy and quantum chemical methods. Density function theory calculations of optimized geometry and vibrational spectra have been carried out by Gaussian03, using 6-311G basis set and B3PW91 functional. Based on these results we have discussed the correlation between these vibrational modes and crystalline structure of Epivir. A complete analysis of experimental IR and Raman spectra has been reported on the basis of wave number of the vibrational bands. The IR and the Raman spectra of the molecule based on DFT calculations shows reasonable agreement with the experimental results. The calculated HOMO, LUMO shows that the charge transfer takes place within the molecule.

In this work, we conducted a comparative analysis among toluene, chloroform and pentanol through theoretical analysis of 2-chloro-5,6-dimethyl-3-(methylsulfanyl) quinoxaline (2Cl5,6Dm3MsQ) molecule with the help of Gaussian 09 software, the geometry of the molecule is optimized and studied the geometric properties using density functional theory (DFT) method. By using DFT method the Mulliken charge distribution of 2Cl5,6Dm3MsQ molecule, highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) analysis of the molecule in different solvent atmosphere which are used to establish the energy band gap and the stability of the molecule are analysed. Potential distribution and density distribution of the titled molecule is analysed by the surface mapping to understand the reactivity of the molecule. From all the findings we observed that, the 2Cl5,6Dm3MsQ molecule has good kinetic stability, by the optical property study we can also ensure that, the molecule may have good biological properties and may also use in optoelectronic devices.

In the present work, a combined experimental and theoretical study on ground state molecular structure, spectroscopic and nonlinear optical properties of the thiophene derivative 2,3-d\Diphenyl-5-(thiophen-2-ylmethylidene)-2,5-dihydro-1,2,4-triazin-6(1H)-one is reported. The entire quantum chemical calculations and optimized structural parameters like bond lengths and bond angles, vibrational frequencies and optimized geometry have performed at DFT/B3LYP method with cc-pVDZ and cc-pVTZ basis sets using the Gaussian 09W program package. The calculated results show that the optimized geometry parameters, the theoretical vibrational frequencies and chemical shift values show good agreement with experimental values. The FTIR and FT Raman spectra of the title compound have been recorded in the regions 4000 – 400 cm -1 and 3500 – 100 cm-1, respectively. The calculated harmonic vibrational frequencies have been compared with experimental FT-IR and FT- Raman spectra. The observed and calculated frequencies are found to be in good agreement. In addition, Mulliken atomic charges, local reactivity descriptors such as local softness (sk), Fukui function (fk), global electrophilicity and nucleophilicity of the title compound were calculated and discussed. Besides HOMO–LUMO energy gap and molecular electrostatic potential map were performed. 1H and 13C NMR isotropic chemical shifts are evaluated experimentally. Magnetic susceptibility has been determined for various range of temperature.

In this study, the Fourier Transform infrared (FT-IR) and FT-Raman spectra of 5-chloro-2-Hydroxy-3-Nitro Pyridine (CHNP) have been recorded in the range 4000-400 and 3500-50 cm-1respectively. The quantum mechanical calculations of energies, optimized geometries and fundamental vibrational wave numbers were calculated using the ab initio (HF) and DFT (B3LYP) gradient methods employing 6-311++G (d,p) basis set. The vibrational frequencies which were determined experimentaldata are compared with theoretical calculations. The complete assignments are performed on the basis of total energy distribution (TED) of the vibrational modes. The calculated HOMO-LUMO energy gap reveals that the charge transfer occurs within the molecule. Thermo dynamical properties like entropy, heat capacity, zero-point vibrational energy and Mulliken’s charge analysis have been calculated for CHNP.The most possible interaction is explained using nature bond orbital (NBO) analysis and the potential compound of non-linear optics (NLO) demands the investigation of its structural and bonding features contributing the hyperpolarizability. The optimized geometrical parameters, fundamental vibrational frequencies, IR intensity, Raman activity are calculated using the GAUSSIAN 09W program packages. The molecular docking results were clustered together and represented by the result with the most favourable free energy of binding. Keywords: FTIR; FT-Raman; HF and DFT; HOMO-LUMO; Mulliken charges;Molecular docking

Benzene is mainly used as an intermediate to make other chemicals; its mostly widely-produced derivatives include styrene, which is used to make polymers and plastics . Benzene is also used to make some types of rubbers, lubricants, dyes, detergents, drugs and pesticides. Natural sources of benzene include volcanoes and forest fires. At one time, chlorobenzene is the main precursor for the manufacture of phenol. The major use of chlorobenzene is an intermediate in the production of commodities such as herbicides, dyestuffs, and rubber. Chlorobenzene is also used as high-boiling solvent in many industrial applications as well as in the laboratory . As a continuation of the recent studies on structural and theoretical investigations of some substituted benzene derivatives, the main aspects of this investigation are: Structural analysis, molecular geometries and vibrational spectra of penta chloro nitrobenzene (PCNB) are calculated by applying density functional theory (DFT) and ab initio (HF) computations and thermodynamical parameters, NBO , NLO and Mulliken Charge analyses have been used to give more information regarding charge transfer within the molecules. Thermo dynamical properties like entropy, heat capacity, zero-point vibrational energy and Mulliken’s charge analysis have been calculated for PCNB. The most possible interaction is explained using nature bond orbital (NBO) analysis and the potential compound of non-linear optics (NLO) demands the investigation of its structural and bonding features contributing the hyperpolarizability. Keywords: FTIR; FT-Raman; HF and DFT; Mulliken charges; NBO; NLO *Corresponding author. Tel.:+919443189328, E-mail address: jjmarivu@yahoo.co.in