ncpchem

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===== Exploing the chiral field =====

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The CHFClBr equilibrium geometry, optimised at the scalar relativistic CCSD(T) level (taken from [[http://link.aps.org/doi/10.1103/PhysRevA.65.042508|here]]), was scaled in the range 0.5 - 2.0 and the total and EPV energy
was calculated at the B3LYP level.
As pointed out by Peter the bond stretching will inevitably lead to a breakdown of the SCF model. Indeed one observes that the HOMO-LUMO gap closes
and the SCF did not converge beyond scaling factor 1.4
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The nuclear repulsion energy is evidently not affected by the breakdown of the wavefunction model and drops off as 1/s, where s is the scaling factor.
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The total energy can be fitted to a 5th-order polynomial within the range of validity of the model and has, as expected, a minimum near the scaling factor 1.0.
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The total EPV energy is not the most interesting quantity since the change in the chiral field for all atoms except the central carbon atom is rather complicated.
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More interesting is the contribution to the EPV energy from the central carbon atom. Surprisingly it increases within the range of validity of the model and goes through a minimum around s=0.82. It can be fitted well to a 4th-order polynomial.
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