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High-level Ab Initio Calculations (high-level + ab_initio_calculation)
Selected AbstractsSpectroscopic Properties in the Liquid Phase: Combining High-Level Ab Initio Calculations and Classical Molecular DynamicsCHEMPHYSCHEM, Issue 1 2006Michele Pavone Dr. Abstract We present an integrated computational tool, rooted in density functional theory, the polarizable continuum model, and classical molecular dynamics employing spherical boundary conditions, to study the spectroscopic observables of molecules in solution. As a test case, a modified OPLS-AA force field has been developed and used to compute the UV and NMR spectra of acetone in aqueous solution. The results show that provided the classical force fields are carefully reparameterized and validated, the proposed approach is robust and effective, and can also be used by nonspecialists to provide a general and powerful complement to experimental techniques. [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] High-Level Ab Initio Study of Anion,, Interactions in Pyridine and Pyrazine Rings Coordinated to AgICHEMPHYSCHEM, Issue 3 2008David Quiñonero Dr. Enhanced binding: High-level ab initio calculations (RI,MP2(full)/aug-cc-pVQZ) demonstrate that the anion binding properties of pyridine and pyrazine are dramatically enhanced when it is coordinated to AgI, as shown in the picture. [source] Nonempirical calculations of NMR indirect spin,spin coupling constantsMAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2006-unsaturated aldehydes, : Azomethines of the, Part 1 Abstract Configurational assignment of seven azomethines obtained from the ,-functionally substituted and nonsubstituted ,,,-unsaturated aldehydes has been performed on the basis of experimental measurements and the high-level ab initio calculations of their 1J(C,C) and 1J(C,H), involving the ,-imino carbon that demonstrated the marked stereochemical dependence of both coupling constants upon the orientation of the nitrogen lone pair in the diverse isomers of the title azomethines. Copyright © 2005 John Wiley & Sons, Ltd. [source] Proton affinity of proline and modified prolines using the kinetic method: role of the conformation investigated by ab initio calculationsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2003S. Mezzache The proton affinities of proline, cis -3-methylproline and cis -3-ethylproline have been measured by the kinetic method using an ion trap instrument; the values obtained are 936, 940.5, and 943,kJ,mol,1, respectively. The experimental values are consistent with those obtained by high-level ab initio calculations (B3LYP/6,31+G*//B3LYP/6,31G* and B3P86/6,31+G*//B3LYP/6,31G*). Several conformations of neutral and protonated proline were considered, in particular the endo and exo ring structure and the position of the carboxyl group. These results show the importance of the position of the hydrogen atom of the carboxyl group in determining the most stable protonated proline structure. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||