Nature and evaluation of steric interactions

What is steric repulsion The generic term refers to the space-filling property of atoms and molecules, as manifested in crystal packing densities, molecular collision cross-sections, and other lines of experimental evidence. Indeed, space-filling molecular models are among the most useful tools of the chemistry studenL and atomic radii are among the first properties called to the student s attention to illustrate atomic periodicity trends. 

To perform NBO steric analysis, simply include the STERIC keyword in the NBO keylist. The hrst output section produces a tabulation of steric exchange energy contributions for each occupied NEMO, dE(i) ] and 

As seen in the table, outer valence NLMOs tend to give negative contributions, but the energy of inner core orbitals is strongly increased by anti-symmetrization, so the net steric exchange energy is positive (by 35.44 kcal/mol) 

Next follow the pairwise steric exchange energies [A ,y, dE i,j ) ] for occupied NLMOs i, j and the total disjoint NLMO steric exchange energy from pairwise sum (sum of pairwise AE,- values) as shown in I/0-6.2. 

As before, the pairwise sum is positive (71.54 kcal/mol) and requires comparison to a reference state before inferences can be drawn. (The pairwise-sum values are intrinsically referenced to a different zero than so no particular significance 

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