VESCF-MO studies of molecules containing atoms from the second row of the Periodic Table. II. Properties of the fluorides of silicon, phosphorus, sulphur, and chlorine for a minimal basis set excluding 3d-orbitals

1968 ◽  
Vol 21 (11) ◽  
pp. 2605 ◽  
Author(s):  
RD Brown ◽  
JB Peel
Keyword(s):  
Electronic Structure ◽  
Electronic Structures ◽  
Periodic Table ◽  
Central Atom ◽  
Dipole Moments ◽  
Coulomb Repulsion ◽  
Basis Set ◽  
Orbital Method ◽  
Molecular Orbital Method ◽  
Minimal Basis

A study has been made of the electronic structures of the fluorides of silicon, phosphorus, sulphur, and chlorine by the VESCF molecular-orbital method with a minimal basis set, not including 3d-orbitals on the central atom. It proves possible to understand variations in bond lengths and charges on fluorine ligands, dipole moments, force constants, and some n.q.r. data. The calculations are found to be sensitive to assumptions about scaling factors for monocentric coulomb repulsion integrals and penetration integrals. We have not discovered any justification for including 3d-orbitals in the description of the electronic structure of these molecules.

A semi-empirical molecular orbital scheme to study electron transfer in iron–sulphur proteins

2005 ◽  
Vol 33 (1) ◽  
pp. 20-21 ◽  
Author(s):  
M. Sundararajan ◽  
J.P. McNamara ◽  
M. Mohr ◽  
I.H. Hillier ◽  
H. Wang
Keyword(s):  
Electron Transfer ◽  
Electronic Structure ◽  
Molecular Orbital ◽  
Parametric Method ◽  
Orbital Method ◽  
Molecular Orbital Method ◽  
Semi Empirical

We describe the use of the semi-empirical molecular orbital method PM3 (parametric method 3) to study the electronic structure of iron–sulphur proteins. We first develop appropriate parameters to describe models of the redox site of rubredoxins, followed by some preliminary calculations of multinuclear iron systems of relevance to hydrogenases.

scholarly journals Electronic Structure Calculations of A2Ti2O7(A = Dy, Ho, and Y)

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
H. Y. Xiao
Keyword(s):  
Electronic Structure ◽  
Strong Interaction ◽  
Electronic Structures ◽  
Coulomb Repulsion ◽  
Electronic Structure Calculations ◽  
Generalized Gradient ◽  
Generalized Gradient Approximation ◽  
Structural And Electronic Properties ◽  
Structure Calculations ◽  
Irradiation Resistance

Ab initiocalculations have been performed on titanate pyrochlores A2Ti2O7(A = Dy, Ho, and Y) to investigate their electronic structures. The generalized gradient approximation (GGA) +Uformalism has been used to correct the strong onsite Coulomb repulsion between the localized 4f electrons. The effects of effectiveUvalues on the structural and electronic properties of A2Ti2O7(A = Dy, Ho, and Y) have been discussed. It is shown that Dy2Ti2O7and Ho2Ti2O7exhibit different electronic structures from Y2Ti2O7. The strong interaction between Dy and Ho 4f electrons and O 2p orbitals may increase the covalency of〈Dy–O〉and〈Ho–O〉bonds and decrease their irradiation resistance.

Benchmarking Electronic Structure Methods for Accurate Fixed-Charge Electrostatic Models

2019 ◽  
Author(s):  
Alex Zhou ◽  
Michael Schauperl ◽  
Paul Nerenberg
Keyword(s):  
Electronic Structure ◽  
Gas Phase ◽  
Condensed Phase ◽  
Force Fields ◽  
Dipole Moments ◽  
Fixed Charge ◽  
Basis Set ◽  
Atomic Charges ◽  
Molecular Dipole ◽  
Partial Atomic Charges

<p>The accuracy of classical molecular mechanics (MM) force fields used for condensed phase molecular simulations depends strongly on the accuracy of modeling nonbonded interactions between atoms, such as electrostatic interactions. Some popular fixed-charge MM force fields use partial atomic charges derived from gas phase electronic structure calculations using the Hartree-Fock method with the relatively small 6-31G* basis set (HF/6-31G*). It is generally believed that HF/6-31G* generates fortuitously overpolarized electron distributions, as would be expected in the higher dielectric environment of the condensed phase. Using a benchmark set of 47 molecules we show that HF/6-31G* overpolarizes molecules by just under 10% on average with respect to experimental gas phase dipole moments. The overpolarization of this method/basis set combination varies significantly though and, in some cases, even leads to molecular dipole moments that are lower than experimental gas phase measurements. We further demonstrate that using computationally inexpensive density functional theory (DFT) methods, together with appropriate augmented basis sets and a continuum solvent model, can yield molecular dipole moments that are both more strongly and more uniformly overpolarized. These data suggest that these methods – or ones similar to them – should be adopted for the derivation of accurate partial atomic charges for next-generation MM force fields.<br></p>

The simplified ab initio method calculation of linear polarizability

1973 ◽  
Vol 26 (5) ◽  
pp. 921 ◽  
Author(s):  
RD Brown ◽  
GR Williams
Keyword(s):  
Ab Initio ◽  
Small Molecules ◽  
Basis Set ◽  
Basis Sets ◽  
Orbital Method ◽  
Polarizability Anisotropy ◽  
Minimal Basis ◽  
Hartree Fock ◽  
Numerical Performance ◽  
Experimental Values

The simplified ab-initio molecular-orbital method described previously is particularly suited to the calculation of polarizabilities by the non-perturbative coupled Hartree-Fock technique. Trial calculations on CO and HF, for which comparison with corresponding ab-initio calculations is possible, show that the method gives an adequate numerical performance. Minimal basis set calculations in general tend to give values that are considerably too low because of inadequate flexibility of the basis and this is the origin of the large discrepancy between theory and experiment, especially for small molecules. ��� Results are also reported for N2O and O3. For these larger systems the SAI results with minimal basis sets are noticeably nearer experimental values. The polarizability anisotropy for N2O is particularly well reproduced by the SAI method. �

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