Hartree-Fock calculations and structure predictions

EXPERIMENT 3.5 HARTREE-FOCK CALCULATIONS AND STRUCTURE PREDICTIONS USING SIMPLIFIED BROWN AND GREEN N,N -DISALICYLALDEHYDE-1,3-PROPANEDIIMINENICKEL(ll), [Ni(salpd)], COMPLEXES... 

EXPERIMENT 3.5 HARTREE-FOCK CALCULATIONS AND STRUCTURE PREDICTIONS 69... 

Procedure 3.5 Hartree-Fock Calculations and Structure Predictions Using Simplified Brown and Green JV,JV -disalicylaldehyde-1,3-propanediimine nickel(ll), [Ni(salpd)], Complexes25... 

The Hartree-Fock or self-consistent-field approximation is a simplification useful in the treatment of systems containing more than one electron. It is motivated partly by the fact that the results of Hartree-Fock calculations are the most precise that still allow the notion of an orbital, or a state of a single electron. The results of a Hartree-Fock calculation are interpretable in terms of individual probability distributions for each electron, distinguished by characteristic sizes, shapes and symmetry properties. This pictorial analysis of atomic and molecular wave functions makes possible the understanding and prediction of structures, spectra and reactivities. 

Optimization at the restricted Hartree-Fock (RHF) and DFT (B3LYP) levels in the 6-31G basis set has also contributed to structural clarification of [l,2,5]thiadiazolo[3,4-f][l,2,5]thiadiazole 6 both approaches successfully predict that 6 ought to have planar equilibrium geometry. Direct a3 initio ipsocentric calculations of the total 7t-current density map for 6 permits classification as aromatic according to magnetic criteria. It exhibits a strong and uniform diatropic perimeter circulation, of comparable intensity to the parent monocycle 11 and similar to that of naphthalene <2004JA11202>. 

MINDO is a much more powerful theory when properly parametrized, giving generally better predictions of structures and energies than minimum-basis-set Hartree-Fock calculations. We shall later describe applications of MINDO and similar approaches to borates (Uchida et al., 1985) and to defects in Si02 (Edwards and Fowler, 1985). However, some of the claims made for this semiempirical approach have been strongly criticized (e.g., Pople, 1975). 

In this lab we will perform Hartree-Fock calculations in Spartan 02 to determine the relative energies of simplified versions of the nickel(II) complexes in the triplet and singlet states. Since the green complex is known to be paramagnetic, this information will help in predicting the structure of the complex. 

Accurate predictions of electronic structure require going beyond the independent electron picture given by the Hartree-Fock approximation and it is obvious that correlation and relativistic corrections should be included simultaneously in a coherent scheme. Not unexpectedly, methods that had proven their efficiency in non-relativistic calculations started to be extended to the relativistic domain. To give some examples ... 

So far the Hartree-Fock results have been in good agreement with experimental information. This means that correlation effects have been of only minor importance in predicting structural information. Therefore, one might expect that the fact that the density-functional calculations yield information that is very similar to those of the Hartree-Fock calculations is due to the similarity of the Kohn-Sham and the Hartree-Fock equations, and that structural parameters are in general not strongly influenced by correlation effects. There are,... 

The molecular geometry and electronic structure of 3,4-diaza-l,6,6al" -trithia-pentalene 85a has been studied and compared with the nitrogen-free I,6,6aA -trithiapentalene [98PS35]. Whereas Hartree-Fock calculations predict 85b and 85c to be valence isomers, DFT and MP2 calculations predict the minimum to be of C2v symmetry corresponding to 85a (Scheme 56). 

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