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

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{{:ncpchem:hlgap.jpg?490}}
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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 E<sub>PV</sub> 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(C<sub>1</sub>-Br): 1.976 Å\\ 
r(C<sub>1</sub>-Cl): 1.776 Å\\ 
r(C<sub>1</sub>-H):  1.100 Å\\ 
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{{:ncpchem:nucrep.jpg?490}}
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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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{{:ncpchem:toterg.jpg?490}}
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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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{{:ncpchem:totalepv.jpg?490}}
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The total E<sub>PV</sub> 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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{{:ncpchem:epv_c.jpg?490}}
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More interesting is the contribution to the E<sub>PV</sub> 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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{{:ncpchem:chfclbr.png?190}}
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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(C<sub>1</sub>-Br): 1.945 Å\\ 
r(C<sub>1</sub>-Cl): 1.766 Å\\ 
r(C<sub>1</sub>-H):  1.087 Å\\ 
Total energy: -3206.489586 hartree\\ 
HOMO-LUMO gap: 0.248490 hartree\\ 
Total E<sub>PV</sub> = 1.001E-18 hartree\\ 
E<sub>PV</sub> (central carbon C<sub>1</sub>): 5.523E-20 hartree\\ 
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{{:ncpchem:cb_chfclbr.png?190}}
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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
</file>
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r(C<sub>1</sub>-Br): 4.469 Å\\ 
r(C<sub>1</sub>-Cl): 4.316 Å\\ 
r(C<sub>1</sub>-H):  3.744 Å\\ 
Total energy: -3510.990470 hartree\\ 
HOMO-LUMO gap: 0.242571 hartree\\ 
Total E<sub>PV</sub> = 1.629E-20 hartree\\ 
E<sub>PV</sub> (central carbon C<sub>1</sub>): 2.905E-23 hartree\\ 
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{{:ncpchem:cb2_chfclbr.png?190}}
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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  
</file>
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r(C<sub>1</sub>-Br): 7.035 Å\\ 
r(C<sub>1</sub>-Cl): 6.882 Å\\ 
r(C<sub>1</sub>-H):  6.319 Å\\ 
Total energy: -3815.623118 hartree\\ 
HOMO-LUMO gap: 0.198085 hartree\\ 
Total E<sub>PV</sub> = -9.436E-23 hartree\\ 
E<sub>PV</sub> (central carbon C<sub>1</sub>): -3.737E-25 hartree\\ 
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