scholarly journals Ab initioanalytical Raman intensities for periodic systems through a coupled perturbed Hartree-Fock/Kohn-Sham method in an atomic orbital basis. I. Theory

2013 ◽  
Vol 139 (16) ◽  
pp. 164101 ◽  
Author(s):  
Lorenzo Maschio ◽  
Bernard Kirtman ◽  
Michel Rérat ◽  
Roberto Orlando ◽  
Roberto Dovesi
Keyword(s):  
Atomic Orbital ◽  
Periodic Systems ◽  
Hartree Fock ◽  
Orbital Basis ◽  
Raman Intensities

scholarly journals QM AND AB INITIO INVESTIGATION ON THE HYDROGEN BONDING, NMR CHEMICAL SHIFTS AND SOLVENT EFFECTS ON THE DPPE

2010 ◽  
Vol 7 (3) ◽  
pp. 260-272
Author(s):  
M. Monajjemi ◽  
A. Nouri ◽  
H. Monajemi
Keyword(s):  
Hydrogen Bonding ◽  
Ab Initio ◽  
Atomic Orbital ◽  
Theoretical Data ◽  
Basis Sets ◽  
Stable Complex ◽  
Head Group ◽  
Water Molecules ◽  
Hartree Fock ◽  
Zwitterionic Form

The hydrogen bonding effects that were produced from interaction of membrane lipid dipalmitoylphosphatidyl-ethanolamine (DPPE) with 1-5 water molecules, has been theoretically  investigated through the quantum mechanical calculations at the Hartree-Fock level of theory and the 3-21G, 6-31G and 6-31G* basis sets with the computational package of Gaussian 98. According to the obtained results of the structural optimization of the isolated DPPE in the gas phase, we can see the evidences of interactions in the head group of this macromolecule (from the molecular point of view we have a proton transfer from the ammonium group to the phosphate oxygen of zwitterionic form. As we know that the hydrogen bonding of DPPE with water molecules which have surrounded its head group plays an important role in the permeability of DPPE. So, in order to understand the microscopic physico-chemical nature of this subject we have analyzed bond and torsion angles of DPPE before and after added water molecules.  In this paper we have theoretically studied the complexes DPPE with water molecules which have surrounded its head group. As mentioned before, this theoretically study has been done through Hartree-Fock level of theory by using simple basis sets. Theoretical data shows that the interaction of head group of DPPE with water molecules causes some changes in the geometry of DPPE which were explained by the contribution of zwitterionic form of DPPE macromolecule, and finally hydrated DPPE becomes stable complex. Comparison between theoretical and experimental geometry data of DPPE macromolecule shows that the calculation at the HF/3-21 level of theory produces results which they are in better agreement with the experimental data. Moreover the hydrogen bonding effects on the NMR shielding tensor of selected atoms in the hydrated complexes of DPPE were reported. The ";Gauge Including Atomic Orbitals"; (GIAO) approaches within the SCF-Hartree-Fock approximation have been used in order to investigate the influence of hydrogen bonding of DPPE-water complex on the shielding tensors. Finally, the solvent affects on the stability of DPPE macromolecule, dipole moment and atomic charge of some selected atoms of DPPE molecule was discussed using Onsager model and Merz-Singh-Kolman schema.   Keywords  : Gauge Including Atomic Orbital, DPPE, hydrogen bonding, solvation, quantum mechanics, ab initio

From Atomic Orbitals to Molecular Orbitals and Chemical Bonds

2020 ◽  
pp. 150-187
Author(s):  
Jochen Autschbach
Keyword(s):  
Hydrogen Molecule ◽  
Atomic Orbital ◽  
Plane Waves ◽  
Basis Set ◽  
Orbital Method ◽  
Chemical Bonds ◽  
Atomic Orbitals ◽  
Hartree Fock ◽  
Generalized Matrix

It is shown how an aufbau principle for atoms arises from the Hartree-Fock (HF) treatment with increasing numbers of electrons. The Slater screening rules are introduced. The HF equations for general molecules are not separable in the spatial variables. This requires another approximation, such as the linear combination of atomic orbitals (LCAO) molecular orbital method. The orbitals of molecules are represented in a basis set of known functions, for example atomic orbital (AO)-like functions or plane waves. The HF equation then becomes a generalized matrix pseudo-eigenvalue problem. Solutions are obtained for the hydrogen molecule ion and H2 with a minimal AO basis. The Slater rule for 1s shells is rationalized via the optimal exponent in a minimal 1s basis. The nature of the chemical bond, and specifically the role of the kinetic energy in covalent bonding, are discussed in details with the example of the hydrogen molecule ion.

Electron impact total and ionization cross sections for Sr, Y, Ru, Pd, and Ag atoms

2013 ◽  
Vol 91 (9) ◽  
pp. 744-750 ◽  
Author(s):  
Dhanoj Gupta ◽  
Rahla Naghma ◽  
Bobby Antony
Keyword(s):  
Electron Impact ◽  
Cross Sections ◽  
Optical Potential ◽  
Atomic Orbital ◽  
Atomic Charge ◽  
Ionization Cross ◽  
Charge Densities ◽  
Hartree Fock ◽  
Spherical Complex ◽  
Ionization Cross Sections

Calculation of electron impact total and ionization cross sections for Sr, Y, Ru, Pd, and Ag atoms were performed using spherical complex optical potential and complex scattering potential-ionization contribution methods. The complex optical potential model is formulated from the target parameters and the atomic charge density. The spherical charge densities are in turn derived from the Roothaan–Hartree–Fock wavefunctions defining the atomic orbital of the target. In the present study cross sections are computed in the energy range from ionization threshold to 2000 eV. The results obtained are compared with other theories and measurements wherever available and were found to be quite consistent and uniform. In general, present data show an overall reasonable agreement with other results. Dependence of total cross sections on the number of target electrons and peak of ionization cross section on target parameters were also found to be consistent with previous observations.

scholarly journals Treatment of the exchange interactions in Hartree-Fock LCAO calculations of periodic systems

1988 ◽  
Vol 92 (4) ◽  
pp. 909-913 ◽  
Author(s):  
M. Causa ◽  
R. Dovesi ◽  
R. Orlando ◽  
Cesare Pisani ◽  
V. R. Saunders
Keyword(s):  
Exchange Interactions ◽  
Periodic Systems ◽  
Hartree Fock
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