scholarly journals Ab initio studies on complexes formed by melamine and cyclotrione

2007 ◽  
Vol 72 (4) ◽  
pp. 375-382 ◽  
Author(s):  
Liangiang Zhu ◽  
Qiwen Teng ◽  
Shi Wu
Keyword(s):  
Ir Spectra ◽  
Ab Initio ◽  
Electronic Properties ◽  
Electronic Spectra ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Binding Energies ◽  
Basis Sets ◽  
Ab Initio Methods ◽  
Ir And Raman

Ab initio methods were used to study the binding energies of non-bonded complexes formed by melamine and cyclotrione, with the STO-3G, 3-21G and 6-31G (d) basis sets. The electronic spectra were computed using the INDO/CIS method, and the IR spectra, Raman and NMR spectra with the RHF/6-31G (d)method. It was demonstrated that the complexes could be formed because of the negative binding energies, which were changed with the change in the electronic properties of the monomers. A red-shift of the first absorptions in the electronic spectra and the vibrational frequencies of the N-H bonds in the IR and Raman spectra of the complexes, compared with those of the monomers, occurred; simultaneously, the 1Hand 13C chemical shifts were altered, due to the non-bonded interaction. .

Experimental Gas Phase 1H NMR Spectra and Basis Set Dependence of ab initio GIAOMO Calculations of 1H and 13C NMR Absolute Shieldings and Chemical Shifts of Small Hydrocarbons

2004 ◽  
Vol 59 (10) ◽  
pp. 1153-1176 ◽  
Author(s):  
Thomas Zuschneid ◽  
Holger Fischer ◽  
Thomas Handel ◽  
Klaus Albert ◽  
Günter Häfelinger
Keyword(s):  
Ab Initio ◽  
Gas Phase ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Basis Set ◽  
Basis Sets ◽  
Gaussian Basis Sets ◽  
Phase Measurements ◽  
H Nmr ◽  
Set Up

AbstractHigh-resolution gas phase measurements of 1H NMR spectra at 400 MHz and atmospheric pressure of seven small hydrocarbons are presented. The developed new method and the experimental set-up are described. Ab initio GIAO MO calculations of 1H and 13C NMR absolute shieldings on the HF, MP2 and B3LYP levels using 25 standard gaussian basis sets are reported for these hydrocarbons, based on experimental re distances. The measured gas phase 1H chemical shifts have been converted to an absolute σ0 shielding scale by use of the literature shielding of methane. These and gas phase 13C literature values have been transferred with literature ZPV data to estimated σeexp shieldings which are used to evaluate the basis set dependence of the calculated σe shieldings utilizing linear least squares regressions. Exponential extrapolations of Dunning basis set calculations allow the determination of basis set limits for 1H and 13C shieldings. 1H and 13C chemical shifts have been derived from the HF calculated shieldings with shieldings of TMS which has been geometry optimized and GIAO calculated in each basis. Standard deviations (esd) as low as 0.09 ppm for 1H and 0.76 ppm for 13C calculations have been obtained.The statistically best basis set for simultaneous calculation of 1H and 13C absolute shieldings or relative shifts is 6-311G* within the HF and B3LYP methods. Aiming for highest accuracy and precision, 1H and 13C have to be treated separately. In this case, best results are obtained using MP2/6-311G** or higher for 1H shieldings and MP2/cc-pVTZ for 13C shieldings.

scholarly journals Stable Occupancy of Hydrogen Molecules in Clathrate Hydrates and + THF Clathrate Hydrates Determined by Ab Initio Calculations

2010 ◽  
Vol 2010 ◽  
pp. 1-6 ◽  
Author(s):  
Prasad Yedlapalli ◽  
Sangyong Lee ◽  
Jae W. Lee
Keyword(s):  
Ab Initio ◽  
Binding Energies ◽  
Clathrate Hydrates ◽  
Basis Set ◽  
Large Cavity ◽  
Basis Sets ◽  
Pure Hydrogen ◽  
Point Energy ◽  
Small Cavity ◽  
Hydrogen Molecules

Structure II clathrate hydrates of pure hydrogen and binary hydrates of are studied using ab initio calculations to determine the stable occupancies of small cavities. Ab initio calculations are carried out for a double cavity consisting of one dodecahedron (small cavity) and one hexakaidecahedron (large cavity). These two cavities are attached to each other as in sII hydrates to form a double cavity. One or two molecules are placed in the small cavity and one THF (or 4 molecules) molecule is placed in the large cavity. We have determined the binding energies of the double cavities at the MP2 level using various basis sets (3-21G, 3-21G(2p), 3-21 G(2p), 6-31G, 6-31G(2p), and 6-31 G(2p)). Different basis sets yield different stable occupancies of the small cavity. The results from the highest basis set (6-31 G(2p) with zero point energy corrections) indicate that the single occupancy is slightly more favorable than the double occupancy in both the cases of pure hydrates and THF + double hydrates.

scholarly journals An Ab initio Study on the Convergence of Electronic Properties of SiC Nanotubes

2013 ◽  
Vol 3 ◽  
pp. 69-73
Author(s):  
Kapil Adhikari ◽  
Asok K. Ray
Keyword(s):  
Silicon Carbide ◽  
Ab Initio ◽  
Electronic Properties ◽  
Density Functional ◽  
National Laboratory ◽  
Basis Sets ◽  
Los Alamos National Laboratory ◽  
Exchange Correlation ◽  
Unit Cells ◽  
Hybrid Density Functional

Ab initio calculations of the electronic structures of silicon carbide (SiC) nanotubes represented by clusters are presented. The nanotube clusters of chiralities (3,3) and (5,5) are studied using the hybrid density functional B3LYP (Becke’s 3-parameter and the Lee-Yang-Parr exchange-correlation) and LANL2DZ (Los Alamos National Laboratory double ?) and 3-21G* basis sets. Evolution of electronic properties of silicon carbide (SiC) nanotubes (3, 3) and (5,5) with their length is discussed. The results suggest that the electronic properties of nanotubes change for short tubes of unit cells with lengths varying from 1 to 5. However, the properties do not seem to change significantly after this. Therefore, an infinite silicon carbide (SiC) nanotube can be approximated by a nanotube cluster of 5 unit cells.The Himalayan PhysicsVol. 3, No. 3, July 2012Page : 69-73

The Smallest “Aurophilic Species”

2009 ◽  
Vol 64 (4) ◽  
pp. 388-394 ◽  
Author(s):  
Raphael J. F. Berger
Keyword(s):  
Ab Initio ◽  
Molecular Species ◽  
Structural Parameters ◽  
Relativistic Effects ◽  
Closed Shell ◽  
Basis Sets ◽  
Ab Initio Methods ◽  
Relativistic Treatment ◽  
Highly Correlated ◽  
Formation Energies

The existence of the C2v symmetric closed-shell di[gold(I)]hydronium cation [Au2H]+ (1), is predicted. It is shown that 1 is the smallest possible molecular species containing aurophilic contacts. Equilibrium structural parameters, vibrational frequencies and formation energies of 1 from Au+ and AuH, have been calculated, employing a series of highly correlated but available standard relativistic ab initio methods up to CCSD(T) level of theory and all-electron basis sets of quadruple-ζ quality with double polarizations. Relativistic effects have been taken into account by employing pseudorelativistic electron core potentials (ECP) or a scalar relativistic treatment using a Douglas-Kroll-Heß Hamiltonian of 2nd, 3rd and 4th order (DKH2, DKH3, DKH4).

4,6-Dicarba-8-thia-arachno-nonaborane(10) Revisited. Theoretical Refinement of Its Structure

1999 ◽  
Vol 64 (6) ◽  
pp. 993-1000 ◽  
Author(s):  
Drahomír Hnyk ◽  
Matthias Hofmann ◽  
Paul von Ragué Schleyer
Keyword(s):  
Raman Spectroscopy ◽  
Ab Initio ◽  
Chemical Shifts ◽  
Structural Features ◽  
Ir And Raman Spectroscopy ◽  
Nmr Method ◽  
Ir And Raman ◽  
Rule Out

The structure of the nine-vertex arachno-thiadicarbaborane C2SB6H10 has been established employing the ab initio/IGLO/NMR method. Theoretical IGLO 11B chemical shifts support C and S atom placements at the 4, 6 and 8 positions, respectively, and unambiguously rule out the 4,6,5-C2SB6H10 structural alternative, suggested earlier on the basis of IR and Raman spectroscopy. Important structural features of the 4,6,8-C2SB6H10 geometry include a small B(7)-S(8)-B(9) angle (MP2(fc)/6-31G*: 97.9°) and long S-B bonds (MP2(fc)/6-31G*: 1.905 and 1.924 Å) compared to B-B bonds spanning the 1.71-1.85 Å range.

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