Explicit bonding approach

Such a "general form of wave function is easily written explicitly for each set of values of N, S, and MS- Any appropriate form of approximate wave functions, like determinantal functions composed of one-electron functions ( molecular spin orbitals ), the "bond eigenfunctions" used in the valence bond approach, and so on, is shown to fulfil this requirement. 

Computational methods to study solvent effects on NMR (Sadlej Pecul) and EPR (Barone, Cimino Pavone) parameters are presented and discussed within the PCM as well their generalizations to hybrid continuum/discrete approaches in which the presence of specific interactions (e.g. solute-solvents H-bonds) is explicitly taken into account by including some solvent molecules strongly interacting with the solute. 

Hybridization in an octahedral complex in the valence bond model of coordination ompound the formation of bonds to an octahedral transition metal ion would involve six d sp h /hrid orbitals. In the approach used here the diff( ring syininetry properties of the s, thii p, p and p.. and the d, and d orbitals used in bonding are explicitly taken into account. However, the 3 all of the p and two ol the d metal valence shell orbitals are otill used in o-bond tormation. 

Empirical Valence Bond Methods. - To examine some important questions relating to enzyme action (e.g. to analyse the causes of catalysis, i.e. why an enzymic reaction proceeds faster than the equivalent, uncatalysed reaction in solution), it is necessary to use a method that not only captures the essential details of the chemical reaction, but also includes the explicit effects of the enzyme and solvent enviroment. One notable method in this area is the empirical valence bond (EVB) model.143 In the empirical valence bond approach, resonance structures (for example ionic and covalent resonance forms)... 

Molecular orbital theory differs from valence bond theory in that it does not require the electrons involved in a bond to be localized between two of the atoms in a molecule. Instead, the electron occupies a molecular orbital, which may be spread out over the entire molecule. As in the valence bond approach, the molecular orbital is formed by adding up contributions from the atomic orbitals on the atoms that make up the molecule. This approach, which does not explicitly model bonds as existing between two atoms, is somewhat less appealing to the intuition than the valence bond approach. However, molecular orbital calculations typically yield better predictions of molecular structure and properties than valence bond methods. Accordingly, most commercially available quantum chemistry software packages rely on molecular orbital methods to perform calculations. 

Jameson and Gutowsky used the independent electron molecular orbital and the valence bond approaches, including d orbitals explicitly. Their equations were applied extensively to shielding by Letcher and Van Wazer. ... 

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