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Electronic Energy (electronic + energy)
Terms modified by Electronic Energy Selected AbstractsA QSAR analysis of toxicity of Aconitum alkaloidsFUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 6 2004Angélica M. Bello-Ramírez Abstract Biological activity of Aconitum alkaloids may be related to their toxicity rather than to a specific pharmacological action. A Quantitative structure-activity relationships (QSAR) analysis was performed on the following two groups of alkaloids: compounds with an aroyl/aroyloxy group at R14 position (yunaconitine, bulleyaconitine, aconitine, beiwutine, nagarine, 3-acetyl aconitine, and penduline), and compounds with the aroyloxy group at R4 position (N -deacetyllappaconitine, lappaconitine, ranaconitine, N -deacetylfinaconitine, N -deacetylranaconitine). The LD50 (,mol/kg) of the 12 alkaloids were obtained from the literature. LD50 was significantly lower in group 1 than in group 2. The steric and core,core repulsion energies were significantly higher in group 1. The total energy and heat of formation and electronic energies were significantly lower in group 1. The reactivity index of N, C1,, C4, and C6, were similar between groups. The reactivity index of C2, was significantly higher and the reactivity index of C3, and C5, were significantly lower in group 1. Log P and pKa were similar between groups. Molecular weight was significantly higher in group 1. A significant linear relationship was observed between log LD50 and either analgesic log ED50 or local anesthetic log ED50. The LD50/analgesic ED50 obtained from average values was 5.9 for group 1 and 5.0 for group 2. However, the LD50/local anesthetic ED50 was 40.4 and 318, respectively. The study supports that the analgesic effects of these alkaloids are secondary to their toxic effects whereas alkaloids from group 2 are susceptible to be further studied as local anesthetic agents. [source] Erratum: Vikas, B. M. Deb: Ground-state electronic energies and densities of atomic systems in strong magnetic fields through a time-dependent hydrodynamical equationINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2008B. M. Deb No abstract is available for this article. [source] A combined ab initio and Franck-Condon factor simulation study on the photodetachment spectrum of ScO2,JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2009Edmond P. F. Lee Abstract Restricted-spin coupled-cluster single-double plus perturbative triple excitation {RCCSD(T)} potential energy functions (PEFs) of the 2B2 state of ScO2 and the 1A1 state of ScO2, were computed, employing the augmented correlation-consistent polarized-weighted core-valence quadruple-zeta (aug-cc-pwCVQZ) basis set for Sc and augmented correlation-consistent polarized valence quadruple-zeta (aug-cc-pVQZ) basis set for O, and with the outer core Sc 3s23p6 electrons being explicitly correlated. Franck-Condon factors, which include allowance for Duschinsky rotation and anharmonicity, were calculated using the computed RCCSD(T) PEFs, and were used to simulate the first photodetachment band of ScO2,. The simulated spectrum matches well with the corresponding experimental 355 nm photodetachment spectrum of Wu and Wang, J Phys Chem A 1998, 102, 9129, confirming the assignment of the photodetachment spectrum and the reliability of the RCCSD(T) PEFs used. Further calculations on low-lying electronic states of ScO2 gave adiabatic relative electronic energies (Te's) of, and vertical excitation energies (Tv's) to, the 2A1, 2B1, and 2A2 states of ScO2 (from the 2B2 state of ScO2), as well as electron affinities (EAs) and vertical detachment energies (VDEs) to these neutral states from the 1A1 state of ScO2,. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Conformational analysis of arginine in gas phase,A strategy for scanning the potential energy surface effectivelyJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2008Sebastian Schlund Abstract The determination of all possible low-lying energy conformers of flexible molecules is of fundamental interest for various applications. It necessitates a reliable conformational search that is able to detect all important minimum structures and calculates the energies on an adequate level of theory. This work presents a strategy to identify low-energy conformers using arginine as an example by means of a force-field based conformational search in combination with high-level geometry optimizations (RI-MP2/TZVPP+). The methods used for various stages in the conformational search strategy are shown and various pitfalls are discussed. We can show that electronic energies calculated on a DFT level of theory with standard exchange-correlation functionals strongly underestimate the intramolecular stabilization resulting from stacked orientations of the guanidine and carbonyl moiety of arginine due to the deficiency of DFT to describe dispersion effects. In this case by usage of electron correlation methods, low energy conformers comprising stacked arrangements that are counterintuitive become favorable. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Synthesis and alkylation of 5-(3-chlorobenzo[b]thien-2-yl)-4H -1,2,4-triazole-3-thiol under classical and microwave conditions.JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 6 2006AM1 semiemperical calculations for investigating the regioselectivity of alkylation Under microwave irradiation (MWI), 5-(3-chlorobenzo[b]thien-2-yl)-4H -1,2,4-triazole-3-thiol (3) was synthesized in a good yield by intramolecular cyclization of the carbonyl thiosemicarbazide 2. A regioselective S-alkylation of 3 with benzyl chloride or allyl bromide has been achieved by using triethylamine as a base, while other different basic conditions led to a mixture of bis(alkylated) derivatives N4, S- and S, N2 -, under both of classical and MWI conditions. The relative stabilities, charge densities, dipole moments and electronic energies of reactants, transition states and intermediates were calculated by the AM1 method and used for investigating the regioselectivity. [source] Structural polymorphism of pyrazinium hydrogen sulfate: extending chemistry of the pyrazinium salts with small anionsACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2010Armand Budzianowski Two polymorphs (,, ,) of pyrazinium hydrogen sulfate (pyzH+HSO, abbreviated as PHS) with distinctly different hydrogen-bond types and topologies but close electronic energies have been synthesized and characterized for the first time. The ,-polymorph (P212121) forms distinct blocks in which the pyzH+ and HSO ions are interconnected through a network of NH...O and OH...O hydrogen bonds. The ,-form () consists of infinite chains of alternating pyzH+ and HSO ions connected by NH...O and OH...N hydrogen bonds. Density functional theory (DFT) calculations indicate the possible existence of a hypothetical polar P1 form of the ,-polymorph with an unusually high dipole moment. [source] X-ray structure and density functional theory studies of an unexpected product: trans -bis{2-[(2-cyanoethyl)iminomethyl]phenolato}copper(II)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2009Maddalena Corsini The title compound, [Cu(C10H9N2O)2] or [CuII(CYMB)2], (I), was obtained in an attempt to reduce trans -bis(2-{[3,5-bis(trifluoromethyl)phenyl]iminomethyl}phenolato)copper(II), [Cu(TIMB)2], (II), with bis(pentamethylcyclopentadienyl)cobalt(II) [decamethylcobaltocene, Cp*2Co, (III)]. The molecular structure of (I) has the CuII centre located on an inversion centre of the C2/c space group. A density functional theory (DFT) analysis at the B3LYP/Lanl2dz(CuF);6-31G**(CHNO) level performed in order to optimize the structures of the free ligands CYMB, and TIMB,, and the metal complexes [CuI/II(CYMB)2],/0 and [CuI/II(TIMB)2],/0, reproduced well the X-ray diffraction structure and allowed us to infer the insertion of the cyanomethide anion on the 3,5-bis(trifluoromethyl)phenyl system from an evaluation of the Mulliken atomic charges and the electronic energies. [source] Molecular one-electron properties using the multireference Hartree,Fock CI methodINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2008A. M. C. Sobrinho Abstract The recently introduced multireference Hartree,Fock configuration interaction (MRHFCI) method has been applied to the calculation of the dipole moment of the LiH, BH, FH, CO, and H2O molecules. The results obtained indicate that MRHFCI wave functions, much more compact but of the same quality of the orthogonal full CI ones, can provide better dipole moments than the corresponding full CI wave functions. The value of the dipole moments obtained with the MRHFCI wave functions is quite insensitive to the choice of the HF references but the same is not true for the electronic energy. Therefore, further studies are necessary to develop a criterion for selecting a set of HF references which could provide the best values of energy and dipole moment. Also, it would be important to verify if other one-electron properties can be computed with the same degree of accuracy obtained for the dipole moments. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] An accurate total energy density functionalINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2007Baojing Zhou Abstract We propose a new density functional for the evaluation of the total electronic energy by subtracting the Roothaan energy, i.e. the Hartree energy of the density residual, from the Hohenberg,Kohn,Sham (HKS) functional, which is normally used in self-consistent Kohn,Sham (KS) density functional theory (DFT) calculations. Because of the positive semi-definite nature of the Roothaan energy, the resulting Wang,Zhou (WZ) functional always produces a total energy lower than that from the HKS functional and usually converges to the exact total energy from below. Following the same spirit of the Zhou,Wang-, (ZW,) functional in the recently proposed orbital-corrected orbital-free (OO) DFT method (Zhou and Wang, J Chem Phys 2006, 124, 081107), we linearly mix the WZ functional with the HKS functional to allow further systematic error cancellations. The resulting Wang,Zhou-, (WZ,) functional is compared with the ZW, functional in OO-DFT calculations for systems within different chemical environment. We find that the optimal value of , for the WZ, functional is more stable than that of , for the ZW, functional. This is because the WZ functional remedies the oscillatory convergence behavior of the Harris functional and renders the direct evaluation of , for the WZ, functional more plausible in the application of the linear-scaling OO-DFT method for large systems. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Approximate lower bounds of the Weinstein and Temple varietyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2007M. G. Marmorino Abstract By using the Weinstein interval or coupling the Temple lower bound to a variational upper bound one can in principle construct an error bar about the ground-state energy of an electronic system. Unfortunately there are theoretical and calculational issues which complicate this endeavor so that at best only an upper bound to the electronic energy has been practical in systems with more than a few electrons. The calculational issue is the complexity of ,H2, which is necessary in the Temple or Weinstein approach. In this work we provide a way to approximate the ,H2, to any desired accuracy using much simpler ,H,-like information so that the lower bound calculations are more practical. The helium atom is used as a testing ground in which we obtain approximate error bars for the ground-state energy of [,2.904230, ,2.903721] hartree using the variational energy with the Temple lower bound and [,2.919098, ,2.888344] hartree for the Weinstein interval. For comparison, the slightly larger error bars using the exact value of ,H2, are: [,2.904358, ,2.903721] hartree and [,2.919765, ,2.887677] hartree, respectively. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Omeprazole and analogue compounds: a QSAR study of activity against Helicobacter pylori using theoretical descriptors,JOURNAL OF CHEMOMETRICS, Issue 8-10 2002Aline Thais Bruni Abstract Omeprazole and analogues were studied with respect to their activity as inhibitors of urease Helicobacter pylori. Conformational analysis was performed according to the method proposed by Bruni et al. Theoretical descriptors were calculated by an ab initio method (6,31G** basis set). Since several minimum energy structures were obtained for each compound, and the calculated descriptors proved to be sensitive to the structural conformation, different criteria were proposed for conformation selection. Three data sets were generated wherein conformations were grouped according to minimum heat of formation, minimum electronic energy and structural similarity. For these three sets, experimental per cent of control was used to develop quantitative structure,activity models by PLS. Their cross-validation and correlation coefficients were very good (Q2,=,0.97 and R2,=,0.99 on average) and the standard error of validation was much smaller in comparison with results from the literature. Copyright © 2002 John Wiley & Sons, Ltd. [source] High-level ab initio calculations on HGeCl and the equilibrium geometry of the Ã1A, state derived from Franck-Condon analysis of the single-vibronic-level emission spectra of HGeCl and DGeClJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2010Daniel K. W. Mok Abstract CCSD(T) and/or CASSCF/MRCI calculations have been carried out on the X,1A, and Ã1A, states of HGeCl. The fully relativistic effective core potential, ECP10MDF, and associated standard valence basis sets of up to the aug-cc-pV5Z quality were employed for Ge. Contributions from core correlation and extrapolation to the complete basis set limit were included in determining the computed equilibrium geometrical parameters and relative electronic energy of these two states of HGeCl. Based on the currently, most systematic CCSD(T) calculations performed in this study, the best theoretical geometrical parameters of the X,1A, state are re(HGe) = 1.580 ± 0.001 Å, ,e = 93.88 ± 0.01° and re(GeCl) = 2.170 ± 0.001 Å. In addition, Franck-Condon factors including allowance for anharmonicity and Duschinsky rotation between these two states of HGeCl and DGeCl were calculated employing CCSD(T) and CASSCF/MRCI potential energy functions, and were used to simulate Ã1A, , X,1A, SVL emission spectra of HGeCl and DGeCl. The iterative Franck-Condon analysis (IFCA) procedure was carried out to determine the equilibrium geometrical parameters of the Ã1A, state of HGeCl by matching the simulated, and available experimental SVL emission spectra of HGeCl and DGeCl of Tackett et al., J Chem Phys 2006, 124, 124320, using the available, estimated experimental equilibrium (r) structure for the X,1A, state, while varying the equilibrium geometrical parameters of the Ã1A, state systematically. Employing the derived IFCA geometry of re(HGe) = 1.590 Å, re(GeCl) = 2.155 Å and ,e(HGeCl) = 112.7° for the Ã1A, state of HGeCl in the spectral simulation, the simulated absorption and SVL emission spectra of HGeCl and DGeCl agree very well with the available experimental LIF and SVL emission spectra, respectively. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] Interesting properties of Thomas,Fermi kinetic and Parr electron,electron-repulsion DFT energy functional generated compact one-electron density approximation for ground-state electronic energy of molecular systemsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2009Sandor Kristyan Abstract The reduction of the electronic Schrodinger equation or its calculating algorithm from 4N -dimensions to a (nonlinear, approximate) density functional of three spatial dimension one-electron density for an N -electron system, which is tractable in the practice, is a long desired goal in electronic structure calculation. If the Thomas-Fermi kinetic energy (,,,5/3dr1) and Parr electron,electron repulsion energy (,,,4/3dr1) main-term functionals are accepted, and they should, the later described, compact one-electron density approximation for calculating ground state electronic energy from the 2nd Hohenberg,Kohn theorem is also noticeable, because it is a certain consequence of the aforementioned two basic functionals. Its two parameters have been fitted to neutral and ionic atoms, which are transferable to molecules when one uses it for estimating ground-state electronic energy. The convergence is proportional to the number of nuclei (M) needing low disc space usage and numerical integration. Its properties are discussed and compared with known ab initio methods, and for energy differences (here atomic ionization potentials) it is comparable or sometimes gives better result than those. It does not reach the chemical accuracy for total electronic energy, but beside its amusing simplicity, it is interesting in theoretical point of view, and can serve as generator function for more accurate one-electron density models. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009 [source] Orbital-orthogonality constraints and basis-set optimizationJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2006Fabio E. Penotti Abstract A new procedure is presented for introducing arbitrary orbital-orthogonality constraints in the variational optimization of otherwise nonorthogonal multiconfiguration electronic wave functions. It is based on suitable analytical changes to the expressions for the first and second derivatives of the electronic energy with respect to the independent variational parameters, and can be applied in the presence of symmetry constraints. It is tested using a second-derivative optimization procedure, the Optimized Basis Set,Generalized Multiconfiguration Spin-Coupled (OBS-GMCSC) approach, that can treat basis-function exponential parameters as variational parameters, to be optimized simultaneously with configuration, spin-coupling, and orbital coefficients. This enables rigorous optimization of basis-set exponential parameters even for fully orthogonal multiconfiguration wave functions. Test calculations are carried out, with optimized even-tempered basis sets, on Li2 and on the CH radical. For the latter, special attention is paid to the electronic spin density at the nuclei. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 762,772, 2006 [source] The OH, + CH3SH reaction: Support for an addition-elimination mechanism from ab initio calculationsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2005Pedro L. Muiño Abstract Several intermediates for the CH3SH + OH, , CH3S, + H2O reaction were identified using MP2(full) 6-311+g(2df,p) ab initio calculations. An adduct, CH3S(H)OH,, I, with electronic energy 13.63 kJ mol,1 lower than the reactants, and a transition state, II,, located 5.14 kJ mol,1 above I, are identified as the entrance channel for an addition-elimination reaction mechanism. After adding zero-point and thermal energies, ,H(reactants , I) = ,4.85 kJ mol,1 and ,H(I , II,) = +0.10 kJ mol,1, which indicates that the potential energy surface is broad and flat near the transition state. The calculated imaginary vibrational frequency of the transition state, 62i cm,1, is also consistent with an addition,elimination mechanism. These calculations are consistent with experimental observations of the OH, + CH3SH reaction that favored an addition,elimination mechanism rather than direct hydrogen atom abstraction. An alternative reaction, CH3SH + OH, , CH3SOH + H,, with ,H = +56.94 kJ mol,1 was also studied, leading to a determination of ,H(CH3SOH) = ,149.8 kJ mol,1. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 612,618, 2005 [source] | ||||||||||