Linear Approximation of Basis Set Orbital Exponents for Isoelectronic Series of Atoms

2004 ◽  
Vol 45 (1) ◽  
pp. 1-4
Author(s):  
Yu. B. Malykhanov ◽  
V. V. Meshkov
Keyword(s):  
Linear Approximation ◽  
Basis Set ◽  
Isoelectronic Series ◽  
Orbital Exponents

Polarization Gaussian p Functions for the Beryllium Atom: Ab initio Calculations on BeH2 and BeH+

1975 ◽  
Vol 53 (22) ◽  
pp. 2512-2516 ◽  
Author(s):  
P. G. Mezey ◽  
I. G. Csizmadia ◽  
O. P. Strausz
Keyword(s):  
Excited State ◽  
Ab Initio Calculations ◽  
Ab Initio ◽  
Ground State ◽  
Optimization Procedure ◽  
Energy Functional ◽  
Basis Set ◽  
Negative Ion ◽  
Gaussian Basis Set ◽  
Orbital Exponents

A set of Gaussian p orbital exponents was obtained by optimizing a (9s5p) Gaussian basis set for an excited state of the beryllium atom and the ground state of the beryllium negative ion. In the optimization procedure the method of conjugate gradients was applied for the energy functional. The optimum (9s5p) basis set was tested on the BeH2 and BeH+ structures.

An ab initio study of the H2O-mediated 1,3-hydrogen rearrangement in the isoelectric series: X, Y = CH2, NH, or O

1991 ◽  
Vol 69 (10) ◽  
pp. 1589-1599 ◽  
Author(s):  
Raymond A. Poirier ◽  
Dake Yu ◽  
Peter R. Surjan
Keyword(s):  
Ab Initio ◽  
Solvent Effects ◽  
Basis Set ◽  
Correlation Effects ◽  
Ab Initio Study ◽  
Reaction Field ◽  
Effect Of Solvent ◽  
Isoelectronic Series ◽  
Intramolecular Hydrogen ◽  
Hydrogen Rearrangement

Ab initio calculations are performed to investigate the effect of water on the 1,3-intramolecular hydrogen rearrangement in the [Formula: see text] isoelectronic series, for X, Y = CH2, NH or O, by modeling with a single H2O molecule. The geometries for the complexes are optimized at both the 3-21G and 6-31G** basis set levels. MP2 and some MP4 calculations are performed to take into account the correlation effects, and ZPV corrections are calculated at the MNDO level. The results show that the water molecule has a significant effect on the molecules in which hydrogen bonds can be formed or partially formed. The "solvent effects" are also examined using the self-consistent reaction-field (SCRF) approach. A combination of supermolecule and SCRF approach appears to work well at predicting the effect of solvent on relative stabilities and barriers. Key words: tautomerism, ab initio, 1,3-hydrogen rearrangement, solvent effects.

Single-centre molecular orbital calculations on third row hydrides - SeH2 and HBr

1975 ◽  
Vol 28 (5) ◽  
pp. 927 ◽  
Author(s):  
RGAR Maclagan
Keyword(s):  
Molecular Orbital ◽  
Photoelectron Spectroscopy ◽  
Basis Set ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Single Centre ◽  
Minimal Basis ◽  
Heavy Atoms ◽  
Orbital Energies ◽  
Orbital Exponents

Single-centre molecular orbital calculations are reported for SeH2, and HBr using basis sets extending up to 5d orbitals centred on the heavy atoms. The choice of orbitals to be used in extending the basis set and the optimum values for orbital exponents are discussed. Orbital energies comparable with minimal basis set multicentre calculations are obtained for SeH2. The orbital energies are compared with those obtained experimentally by photoelectron spectroscopy. The results suggest that the single-centre method is worthy of consideration when studying the hydrides of the heavier elements.

Density functional theory, Comparative vibrational spectroscopic studies, HOMO-LUMO, and NBO analysis of Trichloro isocyanuric acid and Trithio cyanuric acid

2015 ◽  
Vol 8 (3) ◽  
pp. 2197-2221
Author(s):  
Theraviyum Chithambarathanu ◽  
M. Darathi ◽  
J. DaisyMagdaline ◽  
S. Gunasekaran
Keyword(s):  
Density Functional ◽  
Cyanuric Acid ◽  
Nbo Analysis ◽  
Basis Set ◽  
Potential Energy Distribution ◽  
Point Energy ◽  
Isocyanuric Acid ◽  
Ft Ir ◽  
Homo Lumo ◽  
Ft Raman

The molecular vibrations of Trichloro isocyanuric acid (C3Cl3N3O3) and Trithio cyanuric acid (C3H3N3S3) have been investigated in polycrystalline sample at room temperature by Fourier Transform Infrared (FT-IR) and FT-Raman spectroscopies in the region 4000-450 cm-1 and 4000-50 cm-1 respectively, which provide a wealth of structural information about the molecules. The spectra are interpreted with the aid of normal co-ordinate analysis following full structure optimization and force field calculations based on density functional theory   (DFT) using standard B3LYP / 6-311++ G (d, p) basis set for investigating the structural and spectroscopic properties. The vibrational frequencies are calculated and the scaled values are compared with experimental FT-IR and FT-Raman spectra. The scaled theoretical wave numbers shows very good agreement with experimental ones. The complete vibrational assignments are performed on the basis of potential energy distribution (PED) of vibrational modes, calculated with scaled quantum (SQM) method. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The results show that change in electron density (ED) in σ* and π* anti-bonding orbitals and second order delocalization   energy (E2) confirm the occurrence of Intra molecular Charge Transfer (ICT) within the molecule. The thermodynamic properties like heat capacity, entropy, enthalpy and zero point energy have been calculated for the molecule. The frontier molecular orbitals have been visualized and the HOMO-LUMO energy gap has been calculated. The Molecular Electrostatic Potential (MEP) analysis reveals the sites for electrophilic attack and nucleophilic reactions in the molecule.

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