Ab Initio Hartree-Fock Research Articles

Substitution effects and electronic properties of the azo dye (1-phenylazo-2-naphthol) species: a TD-DFT electronic spectra investigation

DFT/B3LYP and ab initio Hartree–Fock calculations with full geometry optimization have been carried out on hydrazo and azo forms of 1-phenylazo-2-naphthol and their substituted derivatives. The predicted geometries show that a small energy difference of 1.8 kcal/mol might tune the equilibrium between both forms. Depending on the electron donating and electron accepting of the different used substituents (CF3, NH2, CH3, Cl, and NO2), the various obtained isomers show small energy differencies between meta and para substitution except for the NH2 one, indicating the coexistence of the tautomers in solution. The ortho(C12) position was found to be the less favored substitution in all cases, while the second ortho(C16) position for different substituents provides isomers competing with the most stable meta and para ones. The obtained results suggest that a judicious choice in the substituents’ use on the phenyl ring should lead to stabilization. The TD-DFT theoretical study performed on the optimized geometry allowed us to identify quite clearly the spectral position and the nature of the different electronic transitions according to their molecular orbital localization, hence, reproducing the available UV-Vis spectra. The increase in the wavelength values is in perfect agreement with red shifts and the ΔE (ELUMO – EHOMO) decreasing. Thus, from the point of view of both substitution and the used solvent, the obtained electronic spectra appear to behave quite differently.

Molecular structure, spectroscopic characterization of (S)-2-Oxopyrrolidin-1-yl Butanamide and ab initio, DFT based quantum chemical calculations

The experimental and theoretical spectra of (S)-2-Oxopyrrolidin-1-yl Butanamide (S2OPB) were studied. FT-IR and FT-Raman spectra of S2OPB in the solid phase were recorded and analyzed in the range 4000–450 and 5000–50cm−1 respectively. The structural and spectroscopic analyses of S2OPB were calculated using ab initio Hartree Fock (HF) and density functional theory calculations (B3PW91, B3LYP) with 6-31G(d,p) basis set. A complete vibrational interpretation has been made on the basis of the calculated Potential Energy Distribution (PED). The HF, B3LYP and B3PW91 methods based NMR calculation has been used to assign the 1H NMR and 13C NMR chemical shift of S2OPB. Comparative study on UV–Vis spectral analysis between the experimental and theoretical (B3PW91, B3LYP) methods and the global chemical parameters and local descriptor of reactivity through the Fukui function were performed. Finally the thermodynamic properties of S2OPB were calculated at different temperatures and the corresponding relations between the properties and temperature were also studied.

Spectroscopic and quantum chemical analysis of a natural product – Hayatin hydrochloride

Majority of drugs in use today are natural products, natural product mimics or semi synthetic derivatives. Therefore in recent times, focus on plant research has increased all over the world and large body of evidence has been collected to show immense potential of medicinal plants used in various traditional systems. Therefore, in the present communication to aid that research, structural and spectroscopic analysis of a natural product, an alkaloid Hayatin hydrochloride was performed. Both ab initio Hartree–Fock and density functional theory employing B3LYP with complete relaxation in the potential energy surface using 6-311G (d,p) basis set were used for the calculations. The vibrational frequencies were calculated and scaled values were compared with experimental FT-IR and micro-Raman spectra. The complete assignments were performed on the basis of potential energy distribution. The structure–activity relationship has also been interpreted by mapping electrostatic potential surface, which are valuable information for the quality control of medicines and drug-receptor interactions. Electronic properties have been analysed employing TD-DFT for both gaseous and solvent phase. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis.

Electronic structure investigations of 4-aminophthal hydrazide by UV–visible, NMR spectral studies and HOMO–LUMO analysis by ab initio and DFT calculations

Combined experimental and theoretical studies were conducted on the molecular structure and vibrational spectra of 4-AminoPhthalhydrazide (APH). The FT-IR and FT-Raman spectra of APH were recorded in the solid phase. The molecular geometry and vibrational frequencies of APH in the ground state have been calculated by using the ab initio HF (Hartree–Fock) and density functional methods (B3LYP) invoking 6-311+G(d,p) basis set. The optimized geometric bond lengths and bond angles obtained by HF and B3LYP method show best agreement with the experimental values. Comparison of the observed fundamental vibrational frequencies of APH 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 NMR spectra of APH was also reported. The theoretical spectrograms for infrared and Raman spectra of the title molecule have been constructed. 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 (ΔH0→T) for APH were also determined.

Molecular Structure, Vibrational Assignments and Non-Linear Optical Properties of 4,4’ Dimethylaminocyanobiphenyl (DMACB) by DFT and <i>ab Initio</i> HF Calculations

In the present study, structural properties of 4,4’ dimethylaminocyanobiphenyl (DMACB) have been studied extensively by using ab initio Hartree Fock (HF) and density functional theory (DFT) employing B3LYP/B3PW91 exchange correlation levels of theory. The vibrational frequencies of DMACB in the ground state have been calculated by using Hartree Fock level and density functional method (B3LYP/B3PW91) with 6-31G(d, p), basis set. Nonlinear optical (NLO) behavior of the examined molecule is investigated by the determination of the electric dipole moment μ, the polarizability α, and the hyperpolarizability β by using the B3LYP/B3PW91 methods.

Molecular structure and vibrational assignment of 1-[N-(2-pyridyl) aminomethylidene}-2(1H)-Naphtalenone by density functional theory (DFT) and ab initio Hartree–Fock (HF) calculations

The molecular geometry and vibrational frequencies of 1-[N-(2-pyridyl)aminomethylidene}-2(1H)-Naphtalenone in the ground state have been calculated by using the Hartree–Fock (HF) and density functional method (B3LYP) with 6-311++G(d,p) basis set. The results of the optimized molecular structure are presented and compared with the experimental X-ray diffraction. The computed vibrational frequencies were used to determine the types of molecular motions associated with each of the experimental bands observed. In addition, calculated results are related to the linear correlation plot of computed data versus experimental geometric parameters and IR data. From the results it was concluded that the B3LYP method is superior to the HF method for the vibrational frequencies. Using the time-dependent density functional theory (TD-DFT) and Hartree–Fock (TD-HF) methods, electronic absorption spectra of the title compound have been predicted and a good agreement with the TD-DFT method and experimental ones is determined.

Polyradical character and spin frustration in fullerene molecules: an ab initio non-collinear Hartree-Fock study.

Most ab initio calculations on fullerene molecules have been carried out on the basis of the paradigm of the Hückel model. This is consistent with the restricted nature of the independent-particle model underlying such calculations, even in single-reference-based correlated approaches. Notwithstanding, previous works on some of these molecules using model Hamiltonians have clearly indicated the importance of short-range interatomic spin-spin correlations. In this work, we consider ab initio non-collinear Hartree-Fock (HF) solutions for representative fullerene systems: the bowl, cage, ring, and pentagon isomers of C20, and the larger C30, C36, C60, C70, and C84 fullerene cages. In all cases but the ring we find that the HF minimum corresponds to a truly non-collinear solution with a torsional spin density wave. Optimized geometries at the generalized HF (GHF) level lead to fully symmetric structures, even in those cases where Jahn-Teller distortions have been previously considered. The nature of the GHF solutions is consistent with the π-electron space becoming polyradical in nature: each p-orbital remains effectively singly occupied. The spin frustration, induced by the presence of pentagon rings on an otherwise antiferromagnetic background, is minimized at the HF level by aligning the spins with non-collinear arrangements. The long-range magnetic ordering observed is reminiscent of the character of broken symmetry HF solutions in polyacene systems.

A comprehensive account of spectral, Hartree Fock, and Density Functional Theory studies of 2-chlorobenzothiazole

Benzothiazole moiety is found to play an important role in medicinal chemistry with a wide range of pharmacological activities. Herein, a simple, benzothiazole derivative viz., 2-chlorobenzothiazole (2CBT) has been analyzed. The spectroscopic properties of the target compound were examined by FT-IR (4400–450cm−1), FT-Raman (4000–50cm−1), and NMR techniques. The 1H and 13C NMR spectra were recorded in DMSO. Theoretical calculations were performed by ab initio Hartree Fock and Density Functional Theory (DFT)/B3LYP method using varied basis sets combination. The scaled B3LYP/6-311++G(d,p) results precisely complements with the experimental findings. Electronic absorption spectra along with energy and oscillator strength were obtained by TDDFT method. Atomic charges have also been reported. Total density isosurface and total density mapped with electrostatic potential surface (MESP) has been shown.

Theoretical study of 11-thiocyanatoundecanoic acid phenylamide derivatives on corrosion inhibition efficiencies

Ab initio Hartree–Fock (HF) and Density Functional Theory (DFT) B3LYP methods with the 6-311G(d,p) basis set were applied to the three 11-thiocyanatoundecanoic acid phenylamide derivatives as corrosion inhibitors. Inhibition efficiency obtained experimentally followed the following order: N-(4-methoxyphenyl)-11-thiocyanatoundecanamide (N3MPTUA) > N-phenyl-11-thiocyanatoundecanamide (NPTUA) > N-(3-nitrophenyl)-11-thiocyanatoundecanamide (N3NPTUA). The molecular parameters most relevant to their potential action as corrosion inhibitors have been calculated in the neutral and protonated forms: EHOMO, ELUMO, energy gap (ΔE), dipole moment (μD), electronegativity (χ), global hardness (η), and the fraction of electrons transferred from the inhibitor molecule to the metallic atom (ΔN). The results of most of the global reactivity descriptors show that the experimental and theoretical studies agree well, and confirm that N3MPTUA is a better inhibitor than NPTUA or N3NPTUA. In addition, the local reactivity, analyzed through Fukui functions, show that the oxygen and nitrogen atoms will be the main adsorption sites.

Quantum chemical density functional theory studies on the molecular structure and vibrational spectra of mannitol

A collective experimental and theoretical study was conducted on the molecular structure and vibrational spectra of mannitol. The FT-IR and FT-Raman spectra of mannitol were recorded in the solid phase. The molecular geometry, vibrational frequencies, thermodynamic functions and atomic charges of mannitol in the ground state have been calculated by using the ab initio HF (Hartree–Fock) and density functional methods (B3LYP) invoking cc-pVDZ basis set. The complete vibrational assignments were performed on the basis of Total Energy Distribution (TED) of the vibrational modes. The UV absorption spectra of the title compound dissolved in water. Natural bond orbital analysis has been carried out to explain the charge transfer or delocalization of charge due to the intra-molecular interactions. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by GIAO methods. The first order hyperpolarizability (β0) of this novel molecular system and related properties (β, α0 and Δα) of mannitol are calculated using B3LYP/cc-pVDZ and HF/cc-pVDZ methods on the finite-field approach. By using TD-DFT calculation, electronic absorption spectra of the title compound have been predicted and a good agreement with experimental one is established. In addition, the molecular electrostatic potential (MEP) have been investigated using theoretical calculations, the calculated HOMO and LUMO energies shows that the charge transfer within the molecule.

Structural and spectroscopic analysis of 3-[(4-phenylpiperazin-1-yl)methyl]-5-(thiophen-2-yl)-2,3-dihydro-1,3,4-oxadiazole-2-thione with experimental (FT-IR, Laser-Raman) techniques and ab initio calculations

Experimental and theoretical harmonic vibrational frequencies of 3-[(4-phenylpiperazin-1-yl)methyl]-5-(thiophen-2-yl)-2,3-dihydro-1,3,4-oxadiazole-2-thione have been investigated in this paper. Experimental FT-IR (400–4000cm−1) and Laser-Raman spectra (100–4000cm−1) of title compound in solid phase have been recorded. Theoretical vibrational frequencies and geometric parameters (bond lengths and bond angles) have been also calculated using ab initio Hartree Fock (HF), density functional theory (B3LYP hybrid functional) methods with 6-311++G(d,p) basis set, for the first time. Assignments of vibrational frequencies have been performed by potential energy distribution (PED) analysis. Total density of state (TDOS) diagrams analysis has been also presented for title compound. Theoretical optimized geometric parameters and vibrational frequencies have been compared with the corresponding experimental data, and they have been shown to be in a good agreement with each other. Besides, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies have been found.

Theoretical conformational study of 1,1,1-trifluoro-4-mercapto-but-3-ene-2-thione and the importance of intramolecular hydrogen bonding in ground and first electronic excited state

Quantum chemical calculations of energies, geometrical structure, intramolecular hydrogen bonding (HB) and vibrational frequencies of 1,1,1-trifluoro-4-mercapto-but-3-ene-2-thione were carried out by the ab initio Hartree–Fock, Moller–Plesset second-order perturbation (MP2) and density functional theory (DFT) methods with 6-311++G** basis set in gas phase and water solution. The nature of the intramolecular hydrogen bond in the most stable chelated conformers has been studied by using the atoms in molecules theory of Bader, which is based on topological properties of the electron density. Natural bond orbital (NBO) analysis was also performed for better understanding of the nature of intramolecular interactions. The influence of the solvent on the stability order of conformers and the strength of intramolecular HB was considered using Tomasi's polarized continuum model. The HOMA, NICS, PDI, ATI, FLU and FLU π indices as well-established aromaticity indicators are examined. The excited-state properties of intramolecular HB in hydrogen-bonded systems have been investigated theoretically using the time-dependent DFT method. The calculated highest occupied molecular orbital (MO) and lowest unoccupied MO with frontier orbital gap are presented. Further verification of the obtained transition state structures was implemented via intrinsic reaction coordinate analysis.

Reactivity of Pyrimidine on Clean Ru(0001): Experimental and Calculated Infrared Spectra

The chemical behavior of pyrimidine on the (0001) close-packed surface of a Ru single crystal was studied by reflection–absorption infrared spectroscopy (RAIRS) and by Hartree–Fock ab initio calculations. At 95 K, the spectra and theoretical simulations indicate molecular docking at fcc hollow sites, as a π-complex almost parallel to the surface. With increasing coverage, some η4 on-top docked species appear, and for a highly packed monolayer physically adsorbed pyrimidine, with some preferential orientation induced by the chemically bonded species, is also present. Subsequent physisorbed layers, randomly oriented, form as exposure increases. The behavior of adsorbed species with thermal activation is not coverage dependent: annealing a low temperature packed monolayer induces rearrangements toward a denser π-complex layer, at the expense of the other surface species, up to 130 K. At this temperature, a tilted intermediate and 2-pyrimidyl bonded to the surface by dehydrogenated C2 and one N, with loss of resonance, and oriented with the C–N bond tilted toward the surface are also proposed. 2-Pyrimidyl is stable between 130 and 180 K and starts desorbing or decomposing above this temperature. A multilayer formed at low temperature is stable up to 110 K and desorbs by annealing to 120 K. For higher temperatures, the composition of the surface layers is similar to that obtained from thermal activation of a dense monolayer. At 150 K, the surface adlayer has the same composition whether it results from an annealed low-temperature monolayer, an annealed multilayer, or a layer built above the stability limit of the multilayer. The relevance of the results obtained is based on the eventual extrapolation to the interactions of pyrimidinic ring molecules with ruthenium.

Experimental and computational study on molecular structure and vibrational analysis of an antihyperglycemic biomolecule: Gliclazide

In present study, the experimental and theoretical harmonic vibrational frequencies of gliclazide molecule have been investigated. The experimental FT-IR (400–4000cm−1) and Laser-Raman spectra (100–4000cm−1) of the molecule in the solid phase were recorded. Theoretical vibrational frequencies and geometric parameters (bond lengths and bond angles) have been calculated using ab initio Hartree Fock (HF), density functional theory (B3LYP hybrid function) methods with 6-311++G(d,p) and 6-31G(d,p) basis sets by Gaussian 09W program. The assignments of the vibrational frequencies were performed by potential energy distribution (PED) analysis by using VEDA 4 program. Theoretical optimized geometric parameters and vibrational frequencies have been compared with the corresponding experimental data, and they have been shown to be in a good agreement with each other. Also, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies have been found.

FT-IR and FT-Raman spectra, molecular structure and first-order molecular hyperpolarizabilities of a potential antihistaminic drug, cyproheptadine HCl

Cyproheptadine hydrochloride (CYP HCl) {4-(5H-dibenzo[a,d]-cyclohepten-5-ylidene)-1-methylpiperidine hydrochloride} is a first-generation antihistamine with additional anticholinergic, antiserotonergic, and local-anesthetic properties. The geometry optimization, Mulliken atomic charges and wavenumber and intensity of the vibrational bands of all of the possible modes of CYP HCl have been calculated using ab initio Hartree–Fock (HF) and density functional theory (DFT) employing the B3LYP functional with the 6-311G(d,p) basis set. We have compared the calculated IR and Raman wavenumbers with experimental data. Quantum-chemical calculations of the geometrical structure, energies, and molecular electrostatic potential and NBO analysis of CYP HCl have been performed using the B3LYP/6-311G(d,p) method. The electric dipole moment (μ), static polarizability (α) and the first hyperpolarizability (β) values of the title compound have been computed using HF and DFT methods. The study reveals that the antihistaminic pharmacological property of CYP HCl has a large β value and, hence, may in general have potential applications in the development of non-linear optical materials. The experimental and calculated results for CYP HCl have also been compared with those for mianserin HCl.

Vibrational spectroscopic (FTIR and FT-Raman), first-order hyperpolarizablity, HOMO, LUMO, NBO, Mulliken charge analyses of 2-ethylimidazole based on Hartree–Fock and DFT calculations

The FTIR and FT-Raman spectra of 2-ethylimidazole (2EIDZ) have been recorded in the region 4000–400cm−1 and 3500–50cm−1, respectively. Utilizing the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compound were carried out. The optimized molecular geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities, were calculated by ab initio Hartree–Fock (HF) and density functional theory (DFT/B3LYP) methods with 6-311++G(d,p) basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. A detailed interpretation of the infrared and Raman spectra of 2EIDZ is also reported based on total energy distribution (TED). The values of the total dipole moment (μ) and the first-order hyperpolarizability (β) of the compound were computed. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. Besides, HOMO and LUMO analysis, Mulliken’s charge analysis and several thermodynamic properties have been calculated.

Structural and electronic study of neutral, positive, and negative small rhodium clusters [Rh(n), Rh(n)(+), Rh(n)(-) ; n = 10-13

We have carried out a systematic study for the determination of the structure and the fundamental state of neutral and ionic small rhodium clusters [Rhn, Rhn(+), Rhn(-); n = 10-13] using ab initio Hartree-Fock methods with a LANL2DZ basis set. A range of spin multiplicities is investigated for each cluster. We present the bond lengths, angles, and geometric configuration adopted by the clusters in its minimum energy conformation showing the differences when the clusters have different number of unpaired electrons. Also we report the vertical ionization potential and the adiabatic one calculated by the Koopmans' theorem.

Molecular structure, vibrational spectroscopy, NBO and HOMO, LUMO studies of o-methoxybenzonitrile

In the present study, the FT-IR and FT-Raman spectra of o-methoxybenzonitrile (O-MBN) have been recorded in the region 4000–400cm−1 and 3500–50cm−1, respectively. The fundamental modes of vibrational frequencies of O-MBN are assigned. Theoretical information on the optimized geometry, harmonic vibrational frequencies, infrared and Raman intensities were obtained by means of ab initio Hartree–Fock (HF) and density functional theory (DFT) gradient calculations with complete relaxation in the potential energy surface using 6-311++G(d,p) basis set. The vibrational frequencies which were determined experimentally from the spectral data are compared with those obtained theoretically from ab initio and DFT calculations. A close agreement was achieved between the observed and calculated frequencies by refinement of the scale factors. The infrared and Raman spectra were also predicted from the calculated intensities. Thermodynamic properties like entropy, heat capacity, zero point energy, have been calculated for the molecule. The predicted first hyperpolarizability also shows that the molecule might have a reasonably good non-linear optical (NLO) behavior. The calculated HOMO–LUMO energy gap reveals that charge transfer occurs within the molecule. Stability of the molecule arising from hyper conjugative interactions, charge delocalization have been analyzed using natural bond orbitals (NBO) analysis. Unambiguous vibrational assignment of all the fundamentals was made using the total energy distribution (TED).

Theoretical study of the isotope effects on the detachment thresholds ofSi−

The isotope effects in Si$^-$ bound levels are studied using the multi-configuration Hartree-Fock ab initio approach. Large scale calculations are carried out for the $3p^3\ ^4S^o,\, ^2D^o$ and $^2P^o$ multiplets of Si$^-$ and the $3p^2\ ^3P$ multiplet of Si. We predict an anomalous isotope shift on the electron affinity, dominated by the specific mass shift, with a value of $IS(^e\!\!A)= -0.66(6)$ m$^{-1}$ for the ($30-28$) isotope pair. We also report hyperfine structure parameters for the studied multiplets. Finally, we provide the values of level electric field gradients at the nucleus that could be of interest in a study of the metastable silicon isotopes. Relativistic corrections are estimated using non-relativistic orbitals in the Breit-Pauli and fully relativistic frameworks.

Synthesis and Vibrational Spectroscopic Investigation of Methyl L-Prolinate Hydrochloride: A Computational Insight

ABSTRACT In our present work, methyl L-prolinate hydrochloride has been synthesized from L-proline amino acid and characterized by Fourier transform infrared and Fourier transform Raman spectra via experimental and computational methods. Ab initio Hartree-Fock and density functional theory (B3LYP) calculations have been made for the structure, and atomic charge distributions were also predicted for the title compound by using the 6-311++G(d,p) basis set. Predicted vibrational frequencies have been assigned and compared with experimental Fourier transform infrared and Fourier transform Raman spectra. The thermodynamic properties such as heat capacity, enthalpy, entropy, and Gibbs energy have been calculated at different temperatures. The calculated highest occupied molecular orbital and lowest unoccupied molecular orbital energy show the charge transfer behavior within the molecule.