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aug-cc-pVTZ Basis Sets (aug-cc-pvtz + basis_set)
Selected AbstractsDevelopment of eclipsed and staggered forms in some hydrogen bonded complexesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2009Ali Ebrahimi Abstract Intermolecular hydrogen bonding in X3CH···NH3 (X = H, F, Cl, and Br) complexes has been studied by B3LYP, B3PW91, MP2, MP3, MP4, and CCSD methods using 6-311++G(d,p) and AUG-cc-PVTZ basis sets. These complexes could exist in both eclipsed (EC) and staggered (ST) forms. The differences between binding energies of EC and ST forms are negligible and all EC and ST shapes correspond to minimum stationary states. The order of stabilities of them is in an agreement with the results of atoms in molecules (AIM) and natural bond orbital (NBO) analyses. On the basis of low differences between binding energies, ST forms are more stable than EC forms in all complexes with the exception of Br3CH···NH3, which behaves just opposite. Although the differences between binding energies are negligible, they are consistent with the results of AIM analysis. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] A Combined Gas-Phase Electron Diffraction/Mass Spectrometric Study of the Sublimation Processes of TeBr4 and TeI4: The Molecular Structure of Tellurium Dibromide and Tellurium DiiodideEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 33 2008Sergey A. Shlykov Abstract The sublimation processes of TeBr4 at 471(5) K and TeI4 at 373(5) K were studied with a combined gas-phase electron diffraction and mass spectrometric technique (GED/MS). The mass spectra and the analysis of the GED intensities showed that a contribution of 40(3) mol-% TeBr2, 59(3) mol-% Br2, and 1 mol-% TeBr4 was formed in the vapor over TeBr4(s). Solid tellurium tetraiodide decomposes to form I2(g) and Te(s). A very small contribution of 3.3,±,2.1 mol-% of gaseous TeI2 was also determined by both GED and MS. The "metallic" Te accumulated in the solid phase vaporizes at above ca. 670 K as the predominately Te2 molcular species. Refinement of the GED intensities resulted in rg(Te,Br) = 2.480(5) Å and ,gBr,Te,Br = 99.0(6)° for TeBr2 and rg(Te,I) = 2.693(9) Å and ,g(I,Te,I) = 103.1(22)° for TeI2. The small contribution of TeBr4 observed in the mass spectra of the vapor over TeBr4 could not be observed in the GED data. Geometric parameters and vibrational frequencies for the tellurium dihalides TeX2 with X = F, Cl, Br, and I were calculated with B3LYP, MP2, CCSD, and CCSD(T) methods by using aug-cc-pVTZ basis sets and various core potentials for the tellurium atom. Bonding properties in tellurium dihalides are discussed on the basis of natural bond orbital analyses. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Comparison of some representative density functional theory and wave function theory methods for the studies of amino acidsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2009Wenbo Yu Abstract Energies of different conformers of 22 amino acid molecules and their protonated and deprotonated species were calculated by some density functional theory (DFT; SVWN, B3LYP, B3PW91, MPWB1K, BHandHLYP) and wave function theory (WFT; HF, MP2) methods with the 6-311++G(d,p) basis set to obtain the relative conformer energies, vertical electron detachment energies, deprotonation energies, and proton affinities. Taking the CCSD/6-311++G(d,p) results as the references, the performances of the tested DFT and WFT methods for amino acids with various intramolecular hydrogen bonds were determined. The BHandHLYP method was the best overall performer among the tested DFT methods, and its accuracy was even better than that of the more expensive MP2 method. The computational dependencies of the five DFT methods and the HF and MP2 methods on the basis sets were further examined with the 6-31G(d,p), 6-311++G(d,p), aug-cc-pVDZ, 6-311++G(2df,p), and aug-cc-pVTZ basis sets. The differences between the small and large basis set results have decreased quickly for the hybrid generalized gradient approximation (GGA) methods. The basis set convergence of the MP2 results has been, however, very slow. Considering both the cost and the accuracy, the BHandHLYP functional with the 6-311++G(d,p) basis set is the best choice for the amino acid systems that are rich in hydrogen bonds. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009 [source] A new parallel algorithm of MP2 energy calculationsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2006Kazuya Ishimura Abstract A new parallel algorithm has been developed for second-order Møller,Plesset perturbation theory (MP2) energy calculations. Its main projected applications are for large molecules, for instance, for the calculation of dispersion interaction. Tests on a moderate number of processors (2,16) show that the program has high CPU and parallel efficiency. Timings are presented for two relatively large molecules, taxol (C47H51NO14) and luciferin (C11H8N2O3S2), the former with the 6-31G* and 6-311G** basis sets (1032 and 1484 basis functions, 164 correlated orbitals), and the latter with the aug-cc-pVDZ and aug-cc-pVTZ basis sets (530 and 1198 basis functions, 46 correlated orbitals). An MP2 energy calculation on C130H10 (1970 basis functions, 265 correlated orbitals) completed in less than 2 h on 128 processors. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 407,413, 2006 [source] Molecular Self-Recognition: Rotational Spectra of the Dimeric 2-Fluoroethanol ConformersCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2009Xunchen Liu Abstract Fluoroalcohols show competitive formation of intra- and intermolecular hydrogen bonds, a property that may be crucial for the protein-altering process in a fluoroalcohol/water solution. In this study, we examine the intra- and intermolecular interactions of 2-fluoroethanol (FE) in its dimeric conformers by using rotational spectroscopy and ab initio calculations. Three pairs of homo- and heterochiral dimeric FE conformers are predicted to be local minima at the MP2/6-311++G(d,p) level of theory. They are solely made of the slightly distorted most stable G+g,/G,g+ FE monomer units. Jet-cooled rotational spectra of four out of the six predicted dimeric conformers were observed and unambiguously assigned for the first time. All four observed dimeric conformers have compact geometries in which the fluoromethyl group of the acceptor tilts towards the donor and ensures a large contact area. Experimentally, the insertion of the OH group of one FE subunit into the intramolecular OH,,,F bond of the other was found to lead to a higher stabilisation than the pure association through an intermolecular OH,,,OH link. The hetero- and homochiral combinations were observed to be preferred in the inserted and the associated dimeric conformers, respectively. The experimental rotational constants and the stability ordering are compared with the ab initio calculations at the MP2 level with the 6-311++G(d,p) and aug-cc-pVTZ basis sets. The effects of fluorination and the competing inter- and intramolecular hydrogen bonds on the stability of the dimeric FE conformers are discussed. [source] | ||||||||||