Home About us Contact
|
Home About us Contact | ||
|
|
||
MP2 Methods (mp2 + methods)
Selected AbstractsPentafluorosulfanyl (SF5) Containing Energetic SaltsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2006Haixiang Gao Abstract New quaternary salts of pentafluorosulfanyl-substituted (SF5) N -methylimidazole (1), 4-amino-1,2,4-triazole (3) or pyridine (5) were prepared and characterized. Most of the salts exhibit good thermal stabilities and low melting points placing them in the ionic liquid class. Their densities range between 1.4 and 1.8 g/cm3. The standard enthalpies of formation for the new salts were calculated by the use of computationally feasible DFT(B3LYP) and MP2 methods in conjunction with an empirical approach based on densities of salts. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Cumulative ,-, interaction triggers unusually high stabilization of linear hydrocarbons inside the single-walled carbon nanotubeINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 12 2007T. C. Dinadayalane Abstract The interactions of linear hydrocarbons C2nH4 and C2nH2 (n = 1,4) with a finite-length armchair (5,5) single-walled carbon nanotube have been investigated using HF and MP2 methods in conjunction with 6-31G(d) basis set, and molecular mechanics (MM) with MM2 force field. In all cases, the results obtained at MP2/6-31G(d) level show stabilization of these supramolecular systems, contrary to the repulsive interactions obtained with the HF method. The interaction energies computed using MM with MM2 force field are in close agreement with the results obtained using the MP2/6-31G(d) level. They increase gradually as the length of linear hydrocarbon chain increases. The present study indicates that cumulative ,-, interaction is the origin for the exceptionally high stabilization of the long nanotube-hydrocarbon complexes. Mulliken population analysis reveals a very small charge transfer between the nanotube and the guest. Essentially there is no change in HOMO-LUMO energy gap by the insertion of linear hydrocarbons. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Density functional study of HO(H2O)n (n = 1,3) clustersINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2005Xiu-Li Dong Abstract The hydrogen bonding complexes HO(H2O)n (n = 1,3) were completely investigated in the present study using DFT and MP2 methods at varied basis set levels from 6-31++G(d,p) to 6-311++G(2d,2p). For n = 1 two, for n = 2 two, and for n = 3 five reasonable geometries are considered. The optimized geometric parameters and interaction energies for various complexes at different levels are estimated. The infrared spectrum frequencies and IR intensities of the most stable structures are reported. Finally, thermochemistry studies are also carried out. The results indicate that the formation and the number of hydrogen bonding have played an important role in the structures and relative stabilities of different complexes. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [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] An ab initio theoretical study of electronic structure and properties of 2,-deoxyguanosine in gas phase and aqueous mediaJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 5 2002S. K. Mishra Abstract Molecular geometries of two structural forms of 2,-deoxyguanosine (keto-N9R and keto-N7R, R = the sugar moiety) considering both the C2,-endo and C3,-endo conformations of the sugar ring and those of the complexes of these species with two water molecules each were optimized employing the ab initio RHF procedure. A mixed basis set consisting of the 6-311+G* basis set for the nitrogen atom of the amino group and the 4-31G basis set for all the other atoms was used. The RHF calculations were followed by correlation correction of the total energy at the MP2 level. Both the structural forms of 2,-deoxyguanosine were solvated using the polarized continuum model (PCM) of the self-consistent reaction field (SCRF) theory and the corresponding RHF optimized geometries at the RHF and MP2 levels. Geometry optimization was also performed in aqueous media using the Onsager model at the RHF level using the above-mentioned mixed basis set, and subsequently, using the reoptimized geometries, single-point MP2 calculations were performed. It is found that both the keto-N9R and keto-N7R forms of 2,-deoxyguanosine as well as their complexes with two water molecules each would occur, particularly at the water,air interface. Though the normal Watson,Crick-type base pairing would not be possible with the keto-N7R form of 2,-deoxyguanosine(G*), two other (G*-C and G*-T) base pairing schemes may occur with this form of the nucleoside, which may cause mutation. The present calculated geometry of the keto-N9R form of the anti -conformation of 2,-deoxyguanosine including the dihedral angle ,CN agree satisfactorily with the available crystallographic results. The present results also agree satisfactorily with those obtained by other authors earlier for the keto-N9R form of 2,-deoxyguanosine using B3LYP and MP2 methods employing the 6-31G* basis set. Using transition state calculations, it is shown that tautomerism of guanine and other similar molecules where the tautomers would coexist would be facilitated by the occurrence of the H+ and OH, fragments of water molecules. Further, this coexistence of the two tautomers appears to make the C8 carbon atom located between the N7 and N9 nitrogen atoms susceptible to attack by the OH, group. Thus, an explanation is obtained for the efficient formation of the reaction product 8-hydroxy-2,-deoxyguanosine, which serves as a biomarker for oxidative damage to DNA in biological systems. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 530,540, 2002; DOI 10.1002/jcc.10046 [source] Energetic polymer salts from 1-vinyl-1,2,4-triazole derivativesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2008Hong Xue Abstract Energetic polymers salts from 1-vinyl-1,2,4-triazole derivatives have been synthesized via free radical polymerization of 1-vinyl-1,2,4-triazolium monomer salts or by protonation of poly(1-vinyl-1,2,4-triazole) with inorganic or organic acids. Standard enthalpies of formation of the new monomer salts were calculated using the computationally feasible DFT(B3LYP) and MP2 methods in conjunction with an empirical approach based on densities of salts. Compared with the monomer salts, the polymer salts have good thermal properties with high densities > 1.5 g cm,3. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2414,2421, 2008 [source] | ||||||||||