Pauli repulsive interactions

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... 

As we will see later this difference in the dependence of the attractive and repulsive interaction on co-ordination number will lead to a preference for low coordination numbers for systems that have significant Pauli-repulsive interactions. 

The preference of CO to adsorb with low coordination relates to the very different coordination preferences of the donating interactions versus backdonating interactions. When doubly occupied orbitals interact with the surface, the bonding and antibonding surface fragment orbitals that are formed can both become occupied and the resulting interaction energy becomes weak or repulsive. The Pauli repulsive interaction between doubly occupied orbitals is approximately proportional to N, the adsorbate coordination number ... 

As an illustration of this, the difference between the computed bond energies of F2, which is -260 kJ/mol, and Ng, which is -1000 kJ/mol, is analyzed. In the F2 molecule both the bonding and antibonding repulsive interactions. The only pair of molecular orbitals where electrons exclusively occupy only the bonding orbital is the <75 orbital constructed from the 2p2 atomic orbitals. This results in an overall attractive contribution to the chemical bond. The attractive orbital overlap contribution which is equal to 2A(2p ) =-9.1 eV is counteracted by the Pauli-repulsive interactions due the [Pg.87]

In the absence of Mg +, the interaction between H2 and Ir4 is dominated by the strong Pauli repulsive interaction between the doubly occupied orbitals of H2 and Ir4. In the presence of Mg +, however, the Ir4 is polarized by Mg +, which reduces the electron... 

Themiodynamic stability requires a repulsive core m the interatomic potential of atoms and molecules, which is a manifestation of the Pauli exclusion principle operating at short distances. This means that the Coulomb and dipole interaction potentials between charged and uncharged real atoms or molecules must be supplemented by a hard core or other repulsive interactions. Examples are as follows. 

Multiple M=P bonding in (OC)5M=PR becomes evident with ADF s bond energy analysis in terms of electrostatic interactions, Pauli repulsion, and orbital interactions from which the a,Ti-separation is obtained using a symmetry decomposition scheme [21]. For singlet (OC)5Cr=PR, which has a BDEst of 40.5 kcal/mol, the a- and n-components are 62.4 and 40.9 kcal/mol, respectively. 

Figure 6.2. Potential energy diagram showing the attractive Van der Waals interaction and the repulsive interaction due to Pauli repulsion,...

A similar calculation can be done for ionic crystals. In this case the Coulomb interaction is taken into account, in addition to the van der Waals attraction and the Pauli repulsion. Although the van der Waals attraction contributes little to the three-dimensional lattice energy, its contribution to the surface energy is significant and typically 20-30%. The calculated surface energy depends sensitively on the particular choice of the inter-atomic potential. 

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