Gauge-including Atomic Orbitals Research Articles

Spectroscopic and theoretical studies of 2-acetylbenzo[b]selenophen-3(2H)-one

In the present study, the FT-IR spectrum of 2-acetylbenzo[b]selenophen-3(2H)-one (2ACSeP, C10H8O2Se) has been recorded in the range of 4000–400 cm−1. The molecular structure of 2ACSeP in the ground state has been investigated by the density functional method (B3PW91) with 6-31G(d,p), 6-311G(d,p), 6-311G(2df,p) and 6-311G(3df,3pd) basis sets. From the potential energy surface calculation, there are two conformers, s-cis and s-trans for this molecule. The computational results diagnose the most stable conformer of 2ACSeP as the s-trans form. Making use of the recorded data, the complete vibrational assignments are made and analysis of the observed fundamental bands of molecule is carried out. The complete assignments are performed on the basis of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMF). The molecular stability and bond strength were investigated by applying the natural bond orbital analysis (NBO) and natural localized molecular orbital (NLMO) analysis. The electronic properties, such as excitation energies, absorption wavelength, HOMO and LUMO energies were performed by the time dependent DFT (TD-DFT) approach. The 1H and 13C nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge-including atomic orbital (GIAO) method and compared with experimental results.

Molecular structure, spectroscopic characterization, HOMO and LUMO analysis of PU and PCL grafted onto PEMA-co-PHEMA with DFT quantum chemical calculations

A newly synthesized polycaprolactone (PCL) and polyurethane (PU) polymers, which grafted onto poly (ethylmethacrylate-co-2-hydroxyethyl methacrylate) (PEMA-co-PHEMA) were characterized both theoretically and experimentally. The FTIR and 1H NMR spectra were recorded for the PCL and PU polymers and the experimental values were compared the theoretical values. The molecular structure evaluation, vibrational frequencies and 1H NMR chemical shift values, which carried out by using gauge including atomic orbital (GIAO) approach, of the PCL and PU polymers were calculated by using density functional method (DFT/B3LYP) with 6-311G (d, p) as a basis set in the ground state. The calculated data such as vibrational frequencies and chemical shift values show good agreement with experimental values. Besides, the thermodynamic properties such as rotational temperatures, rotational constants, zero-point vibrational energy, specific heat capacity, thermal energy, entropy, enthalpy, the electronic properties such as HOMO and LUMO energies, and molecular electrostatic potential (MEP) surfaces for the PCL and PU were calculated and interpreted.

Magnetic Shielding, Aromaticity, Antiaromaticity, and Bonding in the Low-Lying Electronic States of Benzene and Cyclobutadiene.

Aromaticity, antiaromaticity, and their effects on chemical bonding in the ground states (S0), lowest triplet states (T1), and the first and second singlet excited states (S1 and S2) of benzene (C6H6) and square cyclobutadiene (C4H4) are investigated by analyzing the variations in isotropic magnetic shielding around these molecules in each electronic state. All shieldings are calculated using state-optimized π-space complete-active-space self-consistent field (CASSCF) wave functions constructed from gauge-including atomic orbitals (GIAOs), in the 6-311++G(2d,2p) basis. It is shown that the profoundly different shielding distributions in the S0 states of C6H6 and C4H4 represent aromaticity and antiaromaticity "fingerprints" which are reproduced in other electronic states of the two molecules and allow classification of these states as aromatic (S0 and S2 for C6H6, T1 and S1 for C4H4) or antiaromatic (S0 and S2 for C4H4, T1 and S1 for C6H6). S2 C6H6 is predicted to be even more aromatic than S0 C6H6. As isotropic shielding isosurfaces and contour plots show very clearly the effects of aromaticity and antiaromaticity on chemical bonding, these can be viewed, arguably, as the most succinct visual definitions of the two phenomena currently available.

A grayanotox-9(11)-ene derivative from Rhododendron brachycarpum and its structural assignment via a protocol combining NMR and DP4 plus application

A growing body of evidence points to the useful roles of computational approaches in the structural characterization of natural products. Rhododendron brachycarpum has been traditionally used for the control of diabetes, hepatitis, hypertension, and rheumatoid arthritis and classified as an endangered species in Korea. A grayanotox-9(11)-ene derivative along with five known diterpenoids, were isolated from the MeOH extract of R. brachycarpum. Extensive 1D and 2D NMR experiments were conducted to establish the 2D structure and relative configuration of the grayanotox-9(11)-ene derivative. Comparison of simulated and experimental ECD spectra resulted in an inconclusive outcome to assign its absolute configuration. Alternatively, gauge-including atomic orbitals (GIAO) NMR chemical shift calculations, with support by the advanced statistical method DP4 plus, and acid hydrolysis were employed to establish its absolute configuration. This work exemplifies how NMR analysis, combined with quantum mechanics calculations, is a viable approach to accomplish structural assignment of minor abundance molecules in lieu of X-ray crystallography or chiroptical approaches.

Study of hydrogen-bonding, vibrational dynamics and structure-activity relationship of genistein using spectroscopic techniques coupled with DFT

The conformational and hydrogen bonding studies of genistein have been performed by combined spectroscopic and quantum chemical approach. The vibrational spectra (FT-IR and FT-Raman), UV–visible and 1H and 13C NMR absorption spectra of genistein have been recorded and examined. The vibrational wavenumbers of optimized geometry and total energy for isolated molecule and hydrogen-bonded dimers of genistein have been determined using the quantum chemical calculation (DFT/B3LYP) with extended 6–311++G (d,p) basis set. The vibrational assignments for the observed FT-IR and FT-Raman spectra of genistein are provided by calculations on monomer and hydrogen-bonded dimer. The quantum theory of atoms in molecules (QTAIM) is used for investigating the nature and strength of hydrogen-bonds. UV–visible spectrum of the genistein was recorded in methanol solvent and the electronic properties were calculated by using time-dependent density functional theory (TD–DFT). The computed HOMO and LUMO energies predicted the type of transition as π → π*. The 1H and 13C NMR signals of the genistein were computed by the Gauge including atomic orbital (GIAO) approach. Natural bond orbital (NBO) analysis predicted the stability of molecules due to charge delocalization and hyper conjugative interactions. NBO analysis shows that there is an OH⋯O inter and intramolecular hydrogen bond, and π → π* transition in the monomer and dimer, which is consistent with the conclusion obtained by the investigation of molecular structure and assignment of UV–visible spectra.

Basis Sets and Nuclear Magnetic Resonance Shielding Effects for Mixing of MWBN and CNTs

Density functional theory calculations (DFT), as well as hybrid methods (B3LYP) and HF method for MWCNTs have been carried out to study structural stability. The geometry of the MWCNTs have been optimized at DFT and HF methods within CCPTZ-CCPVZ, EPR-II, EPR-II, 6-31G* and 6-31++G** basis sets. According to GIAO method, NMR parameters have been evaluated. The Gaussian quantum chemical package is used for all calculations. The gauge including atomic orbital (GIAO) approach was applied for chemical shielding calculations of (5, 5)@(10, 10), (3, 3)@(7, 7), (4, 4)@(8, 8) DWCNTs.

DFT calculations on molecular structure, spectral analysis, multiple interactions, reactivity, NLO property and molecular docking study of flavanol-2,4-dinitrophenylhydrazone

A new flavanol-2,4-dinitrophenylhydrazone (FDNP) was synthesized and its structure was confirmed by FT-IR, FT-Raman, 1H NMR, mass spectrometry and elemental analysis. All quantum chemical calculations were carried out at level of density functional theory (DFT) with B3LYP functional using 6-311++ G (d,p) basis atomic set. UV–Vis absorption spectra for the singlet-singlet transition computed for fully optimized ground state geometry using Time-Dependent-Density Functional Theory (TD-DFT) with CAM-B3LYP functional was found to be in consistent with that of experimental findings. Analysis of vibrational (FT-IR and FT-Raman) spectrum and their assignments has been done by computing Potential Energy Distribution (PED) using Gar2ped. HOMO-LUMO analysis was performed and reactivity descriptors were calculated. Calculated global electrophilicity index (ω = 7.986 eV) shows molecule to be a strong electrophile. 1H NMR chemical shift calculated with the help of gauge-including atomic orbital (GIAO) approach shows agreement with experimental data. Various intramolecular interactions were analysed by AIM approach. DFT computed total first static hyperpolarizability (β0 = 189.03 × 10−30 esu) indicates that title molecule can be used as attractive future NLO material. Solvent induced effects on the NLO properties studied by using self-consistent reaction field (SCRF) method shows that β0 value increases with increase in solvent polarity. To study the thermal behaviour of title molecule, thermodynamic properties such as heat capacity, entropy and enthalpy change at various temperatures have been calculated and reported. Molecular docking results suggests title molecule to be a potential kinase inhibitor and might be used in future for designing of new anticancer drug.

Molecular structure, spectroscopic properties and quantum chemical calculations of 8-t-buthyl-4-methyl-2H-chromen-2-one

This study acquaints the 8-t-buthyl-4-methyl-2H-chromen 2-one (II) of by quantum chemical calculations and spectral ways. The molecular geometry, vibrational frequencies and gauge including atomic orbital (GIAO) 1H and 13C NMR chemical shift values of II in the ground state have been calculated utilizing the density functional method (B3LYP) with the 6-31G(d) basis set. The theoretical vibrational frequencies and chemical shift values display well agreement with experimental values. On the other hand, DFT calculations of molecular electrostatic potentials and frontier molecular orbitals of II were implemented at the B3LYP/6-31G(d) level of theory.

Molecular docking, TG/DTA, molecular structure, harmonic vibrational frequencies, natural bond orbital and TD-DFT analysis of diphenyl carbonate by DFT approach

Vibrational spectral analysis of Diphenyl Carbonate (DPC) is carried out by using FT-IR and FT-Raman spectroscopic techniques. It is found that all vibrational modes are in the expected region. Gaussian computational calculations were performed using B3LYP method with 6–311++G (d, p) basis set. The computed geometric parameters are in good agreement with XRD data. The observation shows that the structure of the carbonate group is unsymmetrical by ∼5° due to the attachment of the two phenyl rings. The stability of the molecule arising from hyperconjugative interaction and charge delocalization are analyzed by Natural Bond Orbital (NBO) study and the results show the lone pair transition has higher stabilization energy compared to all other. The 1H and 13C NMR chemical shifts are calculated using the Gauge-Including Atomic Orbital (GIAO) method with B3LYP/6-311++G (d, p) method. The chemical shifts computed theoretically go very closer to the experimental results. A study on the electronic and optical properties; absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies and Molecular electrostatic potential (MEP) exhibit the high reactivity nature of the molecule. The non-linear optical property of the DPC molecule predicted theoretically found to be good candidate for NLO material. TG/DTA analysis was made and decomposition of the molecule with respect to the temperature was studied. DPC having the anthelmintic activity is docked in the Hemoglobin of Fasciola hepatica protein. The DPC has been screened to antimicrobial activity and found to exhibit antibacterial effects.

Relativistic DFT calculations of structure and 119Sn NMR chemical shifts for bent M[sbnd]Sn[sbnd]C bonding in Power’s metallostannylenes of chromium, molybdenum, tungsten and iron and diaryl stannylenes

Dispersion corrected density functional theory calculations of the metallostannylene complexes [(η5-C5H5)(CO)3M(SnC6H3-2,6-Ar2)] (1–6; M = Cr, Mo, W; Ar = Mes, Trip), [(η5-C5H5)(CO)2Fe(SnC6H3-2,6-Dip2)] (7) and [(η5-C5H5)(CO)2Fe(SnC6H3-2,6-Trip2)] (8) and monomeric diaryl stannylenes [Sn(C6H2-2,6-Mes2-4-Cl)2] (9), [Sn(C6H2-2,6-Mes2-4-SiMe3)2] (10), [Sn(C6H-2,6-Mes2-3,5-iPr2)2] (11), [Sn(C6H3-2,6-Mes2)2] (12) and [Sn(C6H3-2,6-Dip2)2] (13) (Mes = C6H2-2,4,6-Me3; Trip = C6H2-2,4,6-iPr3; Dip = C6H2-2,6-iPr2) have been carried out at the BP86-D3(BJ)/TZ2P/ZORA level of theory. The calculated geometrical parameters of the studied metallostannyles (Power et al., Organometallics 21 (2002) 5622; 30 (2011) 6316) and diaryl stannylenes (Power et al., Organometallics 34 (2015) 2222) are in good agreement with the available experimental values. The bent geometries at tin are consistent with the presence of a divalent Sn(II) center. The M-Sn-C bond angles in metallostannylenes are smaller than CSnC bond angles in diaryl stannylenes. The lengthening of M − Sn bonds and decrease in MSnC bond angles are found in the solvent (benzene) phase geometries optimized. The 119Sn NMR chemical shifts (ppm) have been calculated with the direct implementation of the gauge including atomic orbitals (GIAO) method. The calculated 119Sn chemical shifts with ZORA spin orbit level in gas phase yield reliable results. While switching from ZORA spin orbit level to ZORA scalar level results 119Sn upfield shift of ca. 300–400 ppm. Due to greater percentage s character of Sn lone pair in the chromium complexes [(η5-C5H5)(CO)3M(SnC6H3-2,6-Mes2)] (1) and [(η5-C5H5)(CO)3M(SnC6H3-2,6-Trip2)] (4), the upfield 119Sn NMR chemical shifts are observed. The relationship between computed (δcalcd) 119Sn NMR chemical shifts and 1/ΔE(LUMO-HOMO)) clearly exhibit a linear trend. The difference between 119Sn NMR chemical shifts of metallostannylenes (1–8) and diaryl stannylenes (9–13) has been analyzed. The SnC bonds in diaryl stannylenes are weaker than the SnC bonds in metallostannylenes. The Sn nuclei are more shielded in diaryl stannylenes than in metallostannylenes. As a consequence, the upfield values of 119Sn NMR chemical shifts are observed for diaryl stannylenes both experimentally and theoretically. Upfield 119Sn chemical shifts, which deviate much from the experimental values, are observed for optimized geometries of metallostannylenes in solvent (benzene) phase. The decrease in asymmetric parameter (η) causes a downfield 119Sn NMR chemical shift accompanied by an increase in 119Sn chemical shift anisotropy.

Prediction of 195Pt NMR chemical shifts of dissolution products of H2[Pt(OH)6] in nitric acid solutions by DFT methods: how important are the counter‐ion effects?

(195) Pt NMR chemical shifts of octahedral Pt(IV) complexes with general formula [Pt(NO3 )n (OH)6 - n ](2-) , [Pt(NO3 )n (OH2 )6 - n ](4 - n) (n = 1-6), and [Pt(NO3 )6 - n - m (OH)m (OH2 )n ](-2 + n - m) formed by dissolution of platinic acid, H2 [Pt(OH)6 ], in aqueous nitric acid solutions are calculated employing density functional theory methods. Particularly, the gauge-including atomic orbitals (GIAO)-PBE0/segmented all-electron relativistically contracted-zeroth-order regular approximation (SARC-ZORA)(Pt) ∪ 6-31G(d,p)(E)/Polarizable Continuum Model computational protocol performs the best. Excellent second-order polynomial plots of δcalcd ((195) Pt) versus δexptl ((195) Pt) chemical shifts and δcalcd ((195) Pt) versus the natural atomic charge QPt are obtained. Despite of neglecting relativistic and spin orbit effects the good agreement of the calculated δ (195) Pt chemical shifts with experimental values is probably because of the fact that the contribution of relativistic and spin orbit effects to computed σ(iso) (195) Pt magnetic shielding of Pt(IV) coordination compounds is effectively cancelled in the computed δ (195) Pt chemical shifts, because the relativistic corrections are expected to be similar in the complexes and the proper reference standard used. To probe the counter-ion effects on the (195) Pt NMR chemical shifts of the anionic [Pt(NO3 )n (OH)6 - n ](2-) and cationic [Pt(NO3 )n (OH2 )6 - n ](4 - n) (n = 0-3) complexes we calculated the (195) Pt NMR chemical shifts of the neutral (PyH)2 [Pt(NO3 )n (OH)6 - n ] (n = 1-6; PyH = pyridinium cation, C5 H5 NH(+) ) and [Pt(NO3 )n (H2 O)6 - n ](NO3 )4 - n (n = 0-3) complexes. Counter-anion effects are very important for the accurate prediction of the (195) Pt NMR chemical shifts of the cationic [Pt(NO3 )n (OH2 )6 - n ](4 - n) complexes, while counter-cation effects are less important for the anionic [Pt(NO3 )n (OH)6 - n ](2-) complexes. The simple computational protocol is easily implemented even by synthetic chemists in platinum coordination chemistry that dispose limited software availability, or locally existing routines and knowhow. Copyright © 2016 John Wiley & Sons, Ltd.

Spectral Properties of α and β L Rhamno-Indigo Molecules and Activities Prediction Through NBO Analysis. A DFT Study

Abstract Structural and physical properties such as some spectral features of α-L rhamno-indigo and β-L rhamno-indigo molecules are presented in this paper. Results are compared with those of 5,5'-dichloro-indigo N-β-glycosidic 4-amino-4,6-didesoxyglucose (Akashine A) that exhibits a strong inhibitory activity against various human tumor cell lines. Density functional theory (DFT) using B3LYP functional and 6-31G+(d,p), 6-311+G(2d,p) and cc-pvdz as basis sets was applied to perform these studies. Calculations were carried out both in gas phase and with DMSO as an implicit solvent. Gauge including atomic orbitals (GIAO) approach was used to calculate 1H NMR chemical shifts and Time dependent density functional theory (TD-DFT) calculations were performed to determine the electronic transitions and their nature within the molecules. Moreover, stabilization energies of intra and intermolecular interactions were determined using NBO analyses. Local reactivity descriptors were computed to give insight in the nature of reactive sites. Overall, it has been shown that the nature of the glycosidic linkages has a significant influence on the molecular properties.

Synthesis of 4-((1E, 6E)-7-(4-hydroxy-3-methoxyphenyl)-3, 5-dioxohepta-1, 6-dienyl)-2-methoxyphenyl 4-fluorobenzoate, a novel monoester derivative of curcumin, its experimental and theoretical (DFT) studies

Curcumin (1), isolated as a major component from the chloroform extract of Curcuma longa was converted to its ester derivative 4-((1E, 6E)-7-(4-hydroxy-3-methoxyphenyl)-3,5-dioxohepta-1,6-dienyl)-2-methoxyphenyl 4-fluorobenzoate (2). The compound has been characterized with the help of 1H, 13C NMR, UV, IR and mass spectrometry. The molecular geometry of synthesized compound was calculated in ground state by Density functional theory (DFT/B3LYP) using 6-31G (d,p) basis set. 1H and 13C NMR chemical shifts were calculated in ground state by using Gauge-Including Atomic Orbital (GIAO) approach and these values were correlated with experimental observations. The electronic properties such as HOMO and LUMO energies were calculated using time dependent Density Functional Theory (TD-DFT). Stability of the molecule as a result of hyper conjugative interactions and electron delocalization were analysed using Natural bond orbital (NBO) analysis. Intramolecular interactions were analysed by AIM (Atom in molecule) approach. Global reactivity descriptors were calculated to study the reactive site within molecule. The vibrational wavenumbers were calculated using DFT method and assigned with the help of potential energy distribution (PED). First hyperpolarizability values have been calculated to describe the nonlinear optical (NLO) property of the synthesized compounds. Molecular electrostatic potential (MEP) analysis has also been carried out.

Conformational search, spectral analysis and electronic properties of 5-(4-Pyridinyl)-1,3,4-thiadiazol-2-amine

Comprehensive investigation of molecular geometry and electronic structure of 5-(4-Pyridinyl)-1,3,4-thiadiazol-2-amine in ground as well as in the first excited state has been carried out. The stable conformers of the title compound have been determined from the 3D potential energy scan by varying selected dihedral angles, responsible for conformational flexibility. As the energy difference between the conformers was very small, the relative stability has been confirmed at potentially high-level G2MP2 method. The most stable structure was optimized with B3LYP and M06-2X functional using polarized triple-zeta 6-311++G(d,p), to obtain the ground state structure and calculation of vibrational wavenumbers. Experimental FT-IR and FT-Raman spectra were compared with theoretical spectral data. Dipole moment, polarizability, first static hyperpolarizability and molecular electrostatic potential surface map have been calculated to get a better insight of the properties of title molecule. Frequency-dependent first hyperpolarizability β(−2ω;ω,ω) has also been evaluated to gauge the non-linear optical behavior of the title compound. Natural bond orbital (NBO) analysis has been done to study the stability of the compound arising from charge delocalization. UV–Vis spectrum, possible solvent-solute interaction and electronic properties such as frontier orbitals, band gap energies have been calculated by TD-DFT approach. 1H nuclear magnetic resonance chemical shifts of the title compound were calculated using the Gauge-Including Atomic Orbital (GIAO) method and compared with experimental data.

THE CONFORMATIONAL EFFECT OF 6-MONO-SUBSTITUTED AND 6, 7-DI-SUBSTITUTED DERIVATIVES OF 5, 6, 7, 8-TETRAHYDRODIBENZO [A, C] CYCLO-OCTENE ON 13C CHEMICAL SHIFT

Hartree-Fock (HF) and Density Functional Theory (DFT) methods employed to study the effect of conformational change on the 13 C chemical shifts of 6-mono axial and equatorial substituted and 6,7-di axial-axial, equatorial-equatorial and axial-equatorial substituted derivatives of 5,6,7,8-tetrahydrodibenzo(a,c)cyclo-octene. The geometry of the conformers have been optimized in the gas phase employing the 6-311G(d,p) basis set. The 13 C chemical shifts were calculated by Gauge Including Atomic Orbitals (GIAO) method. The correlation between calculated 13 C chemical shifts in the gas phase and experimental ones in CDCl3 solvent is linear with squared regression coefficient of 0.96. Also the calculated 13 C chemical shift in the gas phase by the HF method shows better correlation with experimental ones compared with DFT method. Calculations of both the paramagnetic and diamagnetic shielding of carbon atoms demonstrate that the difference between experimental 13 C chemical shifts of the axial and equatorial substituted carbon atoms are more due to the paramagnetic than the diamagnetic shielding.

Efficient calculation of nuclear spin-rotation constants from auxiliary density functional theory.

The computation of the spin-rotation tensor within the framework of auxiliary density functional theory (ADFT) in combination with the gauge including atomic orbital (GIAO) scheme, to treat the gauge origin problem, is presented. For the spin-rotation tensor, the calculation of the magnetic shielding tensor represents the most demanding computational task. Employing the ADFT-GIAO methodology, the central processing unit time for the magnetic shielding tensor calculation can be dramatically reduced. In this work, the quality of spin-rotation constants obtained with the ADFT-GIAO methodology is compared with available experimental data as well as with other theoretical results at the Hartree-Fock and coupled-cluster level of theory. It is found that the agreement between the ADFT-GIAO results and the experiment is good and very similar to the ones obtained by the coupled-cluster single-doubles-perturbative triples-GIAO methodology. With the improved computational performance achieved, the computation of the spin-rotation tensors of large systems or along Born-Oppenheimer molecular dynamics trajectories becomes feasible in reasonable times. Three models of carbon fullerenes containing hundreds of atoms and thousands of basis functions are used for benchmarking the performance. Furthermore, a theoretical study of temperature effects on the structure and spin-rotation tensor of the H(12)C-(12)CH-DF complex is presented. Here, the temperature dependency of the spin-rotation tensor of the fluorine nucleus can be used to identify experimentally the so far unknown bent isomer of this complex. To the best of our knowledge this is the first time that temperature effects on the spin-rotation tensor are investigated.

Molecular structure and vibrational and chemical shift assignments of (4R)-5-eno-4,7-epidioxy-3,7-O-methyl-1,2-O-(S)-trichloroethylidene-5,6,8-trideoxy-α-D-threo-1,4-furano-4,7-diulo-octose by DFT and ab initio HF calculations

Elemental analyses, single crystal X-ray diffraction method, and 1H and 13C NMR spectral techniques are used to synthesize and characterize the crystal structure of 4-diethylamino-2-{[4-(3-methyl-3-phenylcyclobutyl)- thiazol-2-yl]-hydrazonomethyl}-phenol. In order to calculate the molecular geometry along with vibrational frequencies and the gauge including atomic orbital (GIAO) 1H and 13C NMR chemical shift values of the title crystal structure in the ground state, the Hartree–Fock (HF) and density functional theory (DFT) methods with 6-311G(d,p) basis sets are utilized. The assignments of the vibrational frequencies are calculated with the help of the potential energy distribution (PED) analysis using the VEDA 4 software. Experimental data are used for comparison. The molecule contains C–H⋯O intra–inter–molecular interactions.

Coupled-cluster theory for atoms and molecules in strong magnetic fields.

An implementation of coupled-cluster (CC) theory to treat atoms and molecules in finite magnetic fields is presented. The main challenges for the implementation stem from the magnetic-field dependence in the Hamiltonian, or, more precisely, the appearance of the angular momentum operator, due to which the wave function becomes complex and which introduces a gauge-origin dependence. For this reason, an implementation of a complex CC code is required together with the use of gauge-including atomic orbitals to ensure gauge-origin independence. Results of coupled-cluster singles-doubles-perturbative-triples (CCSD(T)) calculations are presented for atoms and molecules with a focus on the dependence of correlation and binding energies on the magnetic field.

The Shielding Effect of Carbon Nanotubes on the Chemical Shift of Adsorbates

Abstract Density functional theory (DFT) was employed to study the shielding effect of carbon nanotubes on NMR chemical shifts of various adsorbates. NMR chemical shifts of adsorbates inside/outside carbon nanotubes (CNTs) were calculated using the gauge-including-atomic-orbital (GIAO) method. Our calculations show parabolic correlation between NMR chemical shift and the distance (R) between CNT and adsorbate. In addition, we have found that there exists a negative region compared to free gases. The shielding effect is more pronounced for adsorbates inside CNT than outside; hence, this finding would certainly be useful for spectroscopic identification of species adsorbed inside or outside of CNT.

Synthesis and spectroscopic characterization on 4-(2,5-di-2-thienyl-1H-pyrrol-1-yl) benzoic acid: A DFT approach

A complete structural and vibrational analysis of the 4-(2,5-di-2-thienyl-1H-pyrrol-1-yl) benzoic acid (TPBA), was carried out by ab initio calculations, at the density functional theory (DFT) method. Molecular geometry, vibrational wavenumbers and gauge including atomic orbital (GIAO) 13C NMR and 1H NMR chemical shift values of (TPBA), in the ground state have been calculated by using ab initio density functional theory (DFT/B3LYP) method with 6-311G(d,p) as basis set for the first time. Comparison of the observed fundamental vibrational modes of (TPBA) and calculated results by DFT/B3LYP method indicates that B3LYP level of theory giving yield good results for quantum chemical studies. Vibrational wavenumbers obtained by the DFT/B3LYP method are in good agreement with the experimental data. The study was complemented with a natural bond orbital (NBO) analysis, to evaluate the significance of hyperconjugative interactions and electrostatic effects on such molecular structure. By using TD-DFT method, electronic absorption spectra of the title compound have been predicted and a good agreement with the TD-DFT method and the experimental one is determined. In addition, the molecular electrostatic potential (MEP), frontier molecular orbitals analysis and thermodynamic properties of TPBA were investigated using theoretical calculations.