Pauli steric repulsion

Of two angular configurations possible on the basis of the previous rules, the configuration having smaller Pauli steric repulsions will be more stable. 

Primary steric effects are due to repulsions between electrons in valence orbitals on adjacent atoms which are not bonded to each other. They are believed to result from the interpenetration of occupied orbitals on one atom by electrons on the other, resulting in a violation of the Pauli exclusion principle. All steric interactions raise the energy of the system in which they occur. Their effect on chemical reactivity is to either decrease or increase a rate or equilibrium constant depending on whether steric repulsions are greater in the reactant or in the product (equilibria) or transition state (rate). 

The name steric or Pauli repulsion for AEPauli already suggests it is repulsive (positive, antibonding), in spite of the negative contribution AVPauli. The repulsive character is due to the strongly positive AT0 (see Figure 2). Steric repulsion is evidently a kinetic energy effect and may also be appropriately called kinetic repulsion. 

So far, we have looked at different modes of bonding and how Pauli repulsive orbital interactions may either influence them (2c-2e bond) or be an essential part (2c-3e bond). In this section, we examine a different role of Pauli repulsion, namely, the one it plays in the absence of bonding interactions between groups. Here, it is responsible for the fact that such groups, A and B say, repel each other. Or, to put it in another way, steric repulsion between A and B is a pure quantum effect, caused by the Pauli repulsion between same-spin electrons of the different fragments, such as the well-known two-center, four-electron (2c-4e) repulsion (19) or the two-center, two-same-spin-electron (2c-2sse) repulsive component (20) of the three-electron bond. 

A correct description of Pauli repulsive interactions between valence, subvalence, and core electrons as well as of electrostatic interactions is an essential requirement for accurate quantum chemical predictions. We now show that a proper analysis of steric repulsion—Pauli repulsion in nonbonded... 

EX Exchange energy. Part of the interaction energy between static charge clouds of two subunits, resulting from Pauli exchange between them. Similar to steric repulsion for molecular interactions. 

ADF calculates various chemically meaningful terms that add up to the bond energy, with an adaptation of Morokuma s bond-energy decomposition to the Kohn-Sham MO method. The individual terms are chemically intuitive quantities such as electrostatic energy, steric repulsion, Pauli repulsion, and orbital interactions. The latter are symmetry decomposed according to the Ziegler transition-state method. ... 

The implication is that the steric repulsion (caused by Pauli repulsion) calculated using the frozen configuration wave function introduced in Sect. 2a, is often relieved in the same way as in Cu, by an electron transfer out of a repulsive a orbital into a n orbital that can backdonate into the n of CO. The a orbital that caused the repulsion with the CO 5a due to a large overlap, will now for the same reason be a good acceptor orbital. 

The major barrier forming steric (Pauli exchange) repulsion changes are given for fully relaxed rotation in the six... 

Section 5.3) of steric effects which compared Pauli exchange repulsions for fully relaxed and rigid rotations, we now partition the fully relaxed barrier energy, AE. into partially relaxed energy terms ... 

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