The simulated ab initio molecular orbital (SAMO) method. VII. Extended basis sets for molecules and polymers

1983 ◽  
Vol 79 (7) ◽  
pp. 3424-3433 ◽  
Author(s):  
Brian J. Duke ◽  
Brian O’Leary
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Basis Sets ◽  
Extended Basis

Ab initio molecular orbital study of simple 1,3-dipolar reactions

1976 ◽  
Vol 29 (3) ◽  
pp. 465 ◽  
Author(s):  
D Poppinger
Keyword(s):  
Transition State ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Transition States ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Molecular Orbital Study ◽  
Orbital Study ◽  
Extended Basis ◽  
Optimized Geometries

Ab initio molecular orbital calculations with minimal and extended basis sets have been carried out for the 1,3-dipolar addition of fulminic acid to acetylene, ethylene, ethynamine and propynenitrile. Optimized geometries are reported for the transition states HCNO+C2H2, HCNO+C2H4, HCNO+ C2HNH2, for the adducts isoxazole and 2-isoxazoline, and for nitrosocyclopropene as a possible intermediate. The calculations indicate that (a) these 1,3-dipolar reactions are synchronous processes, (b) the geometry of the transition state is insensitive to substitution and (c) of the isomeric substituted adducts, 5-aminoisoxazole and isoxazole-4-carbonitrile should be formed preferentially.

Ab initio MP2 study of the HF ... ClF complex using various extended basis sets and bond functions

1996 ◽  
Vol 93 (6) ◽  
pp. 333-342
Author(s):  
Josefredo R. Pliego ◽  
Stella M. Resende ◽  
Wagner B. Almeida
Keyword(s):  
Ab Initio ◽  
Basis Sets ◽  
Bond Functions ◽  
Extended Basis

Structures of simple anions from ab initio molecular orbital calculations

1976 ◽  
Vol 29 (8) ◽  
pp. 1635 ◽  
Author(s):  
L Radom
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Basis Set ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Limited Information ◽  
Orbital Theory ◽  
Comparable Quality ◽  
Split Valence ◽  
Theoretical Results

Ab initio molecular orbital theory with the minimal STO-3G and split-valence 4-31G basis sets is used to obtain geometries of 18 anions:OH-, NH2-, HF2-, BH4-, BF4-, C22-, CN-, NCN2-, N3-, NO2-, NO3-, 0CCO2-, CO32-, HCOO-, CH3COO-, C2O42-, C4O42- and C(CN)3-. The theoretical results are compared with experimental results from the literature. The STO-3G basis set performs somewhat worse for anions than for neutral molecules. On the other hand, the 4-31G basis set gives good results and predicts bond lengths to within 0.02� for all the molecules considered. Limited information on bond angle predictions suggests that these are of comparable quality to those for neutral molecules. The tricyanomethanide ion is predicted to be planar.

An ab initio molecular orbital study of the structure and properties of propadienone (methyleneketene)

1978 ◽  
Vol 31 (1) ◽  
pp. 1 ◽  
Author(s):  
L Radom
Keyword(s):  
Carbon Monoxide ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Heat Of Formation ◽  
Basis Sets ◽  
Orbital Theory ◽  
Orbital Interactions ◽  
Planar Molecule ◽  
Split Valence ◽  
Acetylene Carbon

Ab initio molecular orbital theory with minimal (STO-3G) and split- valence (4-31G) basis sets has been used to obtain fully optimized structures for propadienone, allene, butatriene, carbon dioxide, ketene and vinylidene. Propadienone is predicted to be a planar molecule with C2V symmetry. The systematic deficiencies of the STO-3G and 4-31G basis sets have been taken into account in deriving a complete ro structure for propadienone. A striking feature of this structure is the HCH angle (117.°) which is about 5° smaller than the corresponding angle (122.3°) in ketene. An estimate (125 kJ mol-1) of the heat of formation of propadienone is reported. The alternating dipole moment magnitudes in the series H2CO, H2CCO and H2CCCO are explained in terms of orbital interactions. Propadienone is predicted to be considerably (about 135 kJ mol-1) more stable than vinylidene+carbon monoxide but slightly (about 10-20 kJ mol-1) less stable than acetylene+carbon monoxide.

Effect of Intermolecular Hydrogen Bonding on the Nuclear Quadrupole Interaction in Imidazole and its Derivatives as Studied by ab initio Molecular Orbital Calculations

2000 ◽  
Vol 55 (1-2) ◽  
pp. 315-322
Author(s):  
Nobuo Nakamura ◽  
Hirotsugo Masui ◽  
Takahiro Ueda
Keyword(s):  
Hydrogen Bond ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Quadrupole Interaction ◽  
Bond Distance ◽  
Nuclear Quadrupole Interaction ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Imidazole Derivatives ◽  
Nuclear Quadrupole

Ab initio Hartree-Fock molecular orbital calculations were applied to the crystalline imidazole and its derivatives in order to examine systematically the effect of possible N-H---N type hydrogen bond-ing on the nuclear quadrupole interaction parameters in these materials. The nitrogen quadrupole coupling constant (QCC) and the asymmetry parameter (η) of the electric field gradient (EFG) were found to depend strongly on the size of the molecular clusters, from single molecule, to dimer, trimer and to the infinite molecular chain, i.e., crystalline state, implying that the intermolecular N-H -N hydrogen bond affects significantly the electronic structure of imidazole molecule. A certain correla-tion between the QCC of 14N and the N-H bond distance R was also found and interpreted on the basis of the molecular orbital theory. However, we found that the value of the calculated EFG at the hy-drogen position of the N-H group, or the corresponding QCC value of 2 H, increases drastically as R-3 when R is shorter than about 0.1 nm, due probably to the inapplicability of the Gaussian basis sets to the very short chemical bond as revealed in the actual imidazole derivatives. We suggested that the ob-served N-H distances in imidazole derivatives should be re-examined.

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