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Harmonic Frequencies (harmonic + frequency)
Selected AbstractsA DFT study of two diiron (II) synthetic model compounds and their diiron(III) peroxide oxygenation productsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2009R. C. Binning Jr. Abstract Unrestricted density functional theory calculations have been conducted on two diiron(II) synthetic model compounds. Calculations employed the BPW91 and BOP density functionals with both high-spin and broken symmetry low-spin representations of weakly coupled high-spin irons. Comparison of the calculated and crystallographic structures is made, and good agreement is found with both spin representations. Raman spectral data are available for the diiron(III) product of the reaction with O2 to form a bridged peroxide. Calculated harmonic frequencies confirm the experimental assignments. Small geometry differences between the high spin and broken symmetry results are seen in bond lengths, angles, Raman frequencies, and spin densities associated with oxo and peroxo bridges in the diiron(III) oxidation products. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Computational study of titanium (IV) complexes with organic chromophoresINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2006Ivan Kondov Abstract A computational study of small titanium complexes with the chromophores catechol, alizarin, and coumarin 343 is presented. Employing density functional theory (DFT), the ground-state geometries, energies, and harmonic frequencies of the different compounds are calculated. Furthermore, time-dependent DFT and the configuration interaction singles (CIS) method are used to determine excitation energies and excited-state gradients. Based on these results, the character of the excited states as well as electronic-vibrational coupling strengths are analyzed, and the implications for electron-transfer reactions at dye,semiconductor interfaces are discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Fitting complex potential energy surfaces to simple model potentials: Application of the simplex-annealing methodJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2005Raúl A. Bustos Marún Abstract A stochastic method of optimization, which combines simulated annealing with simplex, is implemented to fit the parameters of a simple model potential. The main characteristic of the method is that it explores the whole space of the parameters of the model potential, and therefore it is very efficient in locating the global minimum of the cost function, in addition to being independent of the initial guess of the parameters. The method is employed to fit the complex intermolecular potential energy surface of the dimer of water, using as a reference the spectroscopic quality anisotropic site,site potential of Feller et al. The simple model potential chosen for its reparameterization is the MCY model potential of Clementi et al. The quality of the fit is assessed by comparing the geometry of the minimum, the harmonic frequencies, and the second virial coefficients of the parameterized potential with the reference one. Finally, to prove more rigorously the robustness of this method, it is compared with standard nonstochastic methods of optimization. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 523,531, 2005 [source] Reduced basis set for the gold atom in cluster complexesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2004Harold Basch Abstract To extend the metal cluster size used in interfacing between bulk metals and molecules in ab initio studies of molecular electronics and chemisorption, a reduced size atomic orbital basis set for the gold atom has been generated. Based on the SKBJ relativistic effective core potential set, the three component 5d Gaussian orbital basis set is completely contracted. Comparisons between the full and reduced basis set in Au atom clusters and cluster complexes for geometry, bond distances, dipole moments, atomic charges, spin, bond dissociation energies, lowest energy harmonic frequencies, electron affinities, ionization energies, and density of states distributions show the contracted set to be a viable replacement for the full basis set. This result is obtained using both the B3LYP and BPW91 exchange-correlation potentials in density functional theory. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 899,906, 2004 [source] Energies, structures, and electronic properties of molecules in solution with the C-PCM solvation modelJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2003Maurizio Cossi Abstract The conductor-like solvation model, as developed in the framework of the polarizable continuum model (PCM), has been reformulated and newly implemented in order to compute energies, geometric structures, harmonic frequencies, and electronic properties in solution for any chemical system that can be studied in vacuo. Particular attention is devoted to large systems requiring suitable iterative algorithms to compute the solvation charges: the fast multipole method (FMM) has been extensively used to ensure a linear scaling of the computational times with the size of the solute. A number of test applications are presented to evaluate the performances of the method. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 669,681, 2003 [source] Robust Automatic Bandwidth for Long MemoryJOURNAL OF TIME SERIES ANALYSIS, Issue 3 2001Marc Henry The choice of bandwidth, or number of harmonic frequencies, is crucial to semiparametric estimation of long memory in a covariance stationary time series as it determines the rate of convergence of the estimate, and a suitable choice can insure robustness to some non-standard error specifications, such as (possibly long-memory) conditional heteroscedasticity. This paper considers mean squared error minimizing bandwidths proposed in the literature for the local Whittle, the averaged periodogram and the log periodogram estimates of long memory. Robustness of these optimal bandwidth formulae to conditional heteroscedasticity of general form in the errors is considered. Feasible approximations to the optimal bandwidths are assessed in an extensive Monte Carlo study that provides a good basis for comparison of the above-mentioned estimates with automatic bandwidth selection. [source] Passively mode-locked fiber laser based on symmetrical nonlinear optical loop mirrorLASER PHYSICS LETTERS, Issue 5 2008Z.X. Zhang Abstract We propose and demonstrate a passively mode-locked Erbium-doped fiber laser based on symmetrical nonlinear optical loop mirror. The nonlinear optical loop mirror with intensitydepended transmission can act as an equivalent saturable absorber, which results in passively mode-locking of fiber laser. Pulse trains with fundamental cavity frequency and its various harmonic frequencies have been obtained. (© 2008 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] An improved design of harmonic suppression for microstrip patch antennasMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2007M. K. Mandal Abstract Harmonic suppression is an important factor for active microstrip patch antennas radiating harmonic frequencies. Here, a novel compact low pass filter (LPF) having high filter selectivity and wide stop band is used on the microstrip feed line of the patch antenna. The 15 dB LPF stopband exist over 10 GHz while implementing area is 0.1464,g × 0.1789,g at the cutoff frequency of 3.55 GHz. The fundamental antenna operating frequency falls in the passband of the LPF. The other harmonics falls in the LPF stopband and thus attenuated. An example shows up to fourth harmonic are suppressed while total occupying area remains compact. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 103,105, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22049 [source] Explicitly correlated SCF study of anharmonic vibrations in (H2O)2INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4-5 2002Donald D. Shillady Abstract Modeling solvation in high-pressure liquid chromatography (HPLC) requires calculation of anharmonic vibrational frequencies of solvent clusters for a statistical partition function. An efficient computational method that includes electron correlation is highly desirable for large clusters. A modified version of the "soft Coulomb hole" method of Chakravorty and Clementi has recently been implemented in a Gaussian-lobe-orbital (GLO) program (PCLOBE) to include explicit electron,electron correlation in molecules. The soft Coulomb hole is based on a modified form of Coulomb's law: An algorithm has been developed to obtain the parameter "w" from a polynomial in the effective scaling of each primitive Gaussian orbital relative to the best single Gaussian of the H1s orbital. This method yields over 90% of the correlation energy for molecules of low symmetry for which the original formula of Chakravorty and Clementi does not apply. In this work, all the vibrations of the water dimer are treated anharmonically. A quartic perturbation of the harmonic vibrational modes is constrained to be equal to the exact Morse potential eigenvalue based on a three-point fit. This work evaluates the usefulness of fitting a Morse potential to a hydrogen bond vibrational mode and finds it to be slightly better than using MP2 vibrational analysis for this important dimer. A three-point estimate of the depth, De, of a Morse potential leads to a correction formula for anharmonicity in terms of the perturbed harmonic frequency: When scaled by 0.9141, the harmonic Morse method leads to essentially the same results as scaling the BPW91 local density method by 0.9827. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 [source] | ||||||||||