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

The CCSD(T) optimized geometry is:\\ 
r(C1-Br): 1.976 Å\\ 
r(C1-Cl): 1.776 Å\\ 
r(C1-H): 1.100 Å\\ 
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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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<file CHFXopt.xyz>
 5
scf done: -3172.829144
 C -1.874368 1.699460 -0.238135
Br -2.517620 -0.079089 0.215619
 H -2.245107 1.932961 -1.232587
Cl -2.454927 2.930736 0.887073
 F -0.528269 1.693590 -0.245441
</file>
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r(C1-Br): 1.945 Å\\ 
r(C1-Cl): 1.766 Å\\ 
r(C1-H): 1.087 Å\\ 
Total energy: -3206.489586 hartree\\ 
HOMO-LUMO gap: 0.248490 hartree\\ 
Total EPV = 1.001E-18 hartree\\ 
EPV (central carbon C1): 5.523E-20 hartree\\ 
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<file cb_CHFX_Ropt.xyz>
 13
scf done: -3477.261538
 C -1.712432 1.322399 -0.468191 H 
 C -2.083610 -0.032394 -0.003986 H 
 C -2.498564 1.665678 -1.672890 H 
 C -1.993900 2.307555 0.597662 H 
 C -0.270315 1.354795 -0.798693 H 
 C -3.139942 1.948107 -2.650403 H 
 C -2.225567 3.109877 1.460851 H 
 C -2.385463 -1.125021 0.370581 H 
 C 0.898869 1.383167 -1.067164 L H
Cl -2.539540 4.202586 2.638111 H 
 H 1.935810 1.408304 -1.305458 H 
Br -4.092424 2.366916 -4.103780 H 
 F -2.707154 -2.290764 0.770012 L H
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r(C1-Br): 4.469 Å\\ 
r(C1-Cl): 4.316 Å\\ 
r(C1-H): 3.744 Å\\ 
Total energy: -3510.990470 hartree\\ 
HOMO-LUMO gap: 0.242571 hartree\\ 
Total EPV = 1.629E-20 hartree\\ 
EPV (central carbon C1): 2.905E-23 hartree\\ 
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<file cb2_CHFXopt.xyz>
 21
scf done: -3781.817398
 C -1.569422 1.426972 -0.444525 H 
 C -1.877703 0.020308 -0.116740 H 
 C -2.369353 1.848010 -1.612073 H 
 C -1.896220 2.286398 0.710845 H 
 C -0.132460 1.555677 -0.761518 H 
 C -3.025886 2.193654 -2.567233 H 
 C -2.164591 2.990875 1.656343 H 
 C -2.131541 -1.129727 0.151315 H 
 C 1.043019 1.661785 -1.021021 L H
 C -2.466017 3.781276 2.718191 H 
 C 2.367315 1.781049 -1.313191 H 
 C -3.763495 2.581033 -3.638934 H 
 C -2.417583 -2.425916 0.453469 L H
 C -4.422240 2.926515 -4.595711 H 
 C -2.733502 4.485859 3.664755 H 
 C 3.542557 1.886953 -1.572586 H 
 C -2.670204 -3.569979 0.720249 H 
 H 4.577709 1.980457 -1.801197 H 
Cl -3.094602 5.433954 4.939276 H 
Br -5.390750 3.433046 -5.999501 H 
 F -2.937158 -4.778650 1.002047 H 
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r(C1-Br): 7.035 Å\\ 
r(C1-Cl): 6.882 Å\\ 
r(C1-H): 6.319 Å\\ 
Total energy: -3815.623118 hartree\\ 
HOMO-LUMO gap: 0.198085 hartree\\ 
Total EPV = -9.436E-23 hartree\\ 
EPV (central carbon C1): -3.737E-25 hartree\\ 
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